MXPA05013589A - Durable bn mould separating agents for the die casting of non-ferrous metals - Google Patents

Abstract

The invention relates to corrosion-resistant, temperature-stable, durable mould separating layers, suitable for the die casting of non-ferrous metals, comprising boron nitride and slips for production thereof, a method for production of the slips, a method for production of the mould separating layers and the use of the mould separating layers.

Description

DURABLE BORO NITRIDE MOLD DETACHMENT AGENTS FOR METAL PRESSURE COLLARING NO FERROUS DESCRIPTIVE MEMORY The invention relates to durable, corrosion-resistant, thermally stable mold release layers suitable for pressure casting of non-ferrous metals and comprising boron nitride, and also to sizes for their production, to a process for producing the sizing, to a process for producing the mold release layers and to the use of the mold release layers. Boron nitride is a material that has been known for some time and whose crystalline structure is similar to that of graphite. Like graphite, it has a lower wettability compared to many substances, for example, silicone fused materials, or molten metal materials. Therefore, there have been several investigations on non-beading layers based on boron nitride in order to use them for casting processes. However, the problem with this use is that it is not possible to apply boron nitride in substance to molds, especially of a relatively complex nature, in a lasting manner. The application of boron nitride sintering is avoided by its high sintering temperature. In addition, it is required to apply these layers in a very impermeable manner, so that the molten materials can not penetrate into pores, which can lead to increased adhesion. Therefore, there have been many attempts to employ binders in an inorganic base, where the boron nitride has been bound. In order to survive the temperatures that occur, for example, in the course of metal pressure casting, these binders have to be virtually inorganic in their entirety, since the organic binders decompose or pyrolyze. A disadvantage of these inorganic binders is, when they form impermeable layers, that they can not cover the boron nitride particles and thus reduce or completely nullify the boron nitride antiadhesive powder. This can be avoided sparingly, since the binders according to the prior art, for example, aluminum phosphates, other phosphates or silicates require a type of melt flow to become impermeable, which drastically reduces the anti-tack action of boron nitride, and the binders can in this way react to the liquid metal, which can lead to adhesion of the casting in the release layer. The complex thin-walled components made of non-ferrous metals (aluminum, zinc, brass, magnesium) are currently produced by pressure casting processes. The metallic molten materials are compressed by the application of pressure in the molds generally of multiple parts. These mold parts are generally manufactured from a steel of high tensile strength.

Mold interiors that come into contact with partly melted (semi-solid or thixoformed) or molten metals should be provided with release layers in order to avoid corrosion of the mold wall by liquid metal, to achieve easy demolding by sliding action and lubrication, to avoid lubricant adhesion to prevent the adhesion of the casting (welding) by the formation of barrier, and to ensure a support of the metallic flow when extending the flow trajectories. Important requirements in the release agent are that no solid residue or solid crack product is left behind on the surface of the mold, the workpiece surface or in the cast, which does not lead to an additional increase in gas content ( gaseous fissure products) in the casting, that the separated fissure products do not contain any hazardous or toxic substance and that they do not lead to any adverse influence on the surface properties and mechanical properties of the castings. The modern mold release agents are subdivided into two large groups, first the liquid mold release agents in the form of aqueous or water-soluble or organic (water-insoluble) mold release agents, and secondly the group of dry-release agglomerate powders. The organic mold release agents used are silicon oils, non-polar polyolefins, grease, oils or synthetic or natural waxes, for example, mineral or vegetable or animal oils or waxes, carboxylic acids, organic metal salts, fatty acid esters. and many more. For example, for the casting of iron or steel pressure, ZrÜ2 or a mixture of ZrÜ2 with AI2O3 is used as a release agent in combination with alkali metal silicates. Mold release systems commercially available on the market to date, comprising inorganic release agents, in almost all cases comprise hexagonal boron nitride (BN), M0S2 or graphite as inorganic mold release agents in combination with AI2O3. , alkali metal silicates and alkaline earth metal silicates, and, in some cases, also clays, as described, for example, in US 5,026,422 or US 5,007926. In addition to the organic release agents, the inorganic release agents such as graphite, boron nitride, mica, talc, molybdenum disulfide, molybdenum diselenide, rare earth fluorides, etc. they also find use in pressure casting, as described, for example, in US 2001/0031707 A1, US 3,830,280 or US 5,076,339. JP 57168745 claims a mold release agent for the casting of aluminum in metallic dies, which has good film formation and good corrosion properties with respect to liquid aluminum. The composition comprises boron nitride, mica, talc, vermiculite and organic water soluble binders (CMC).

To improve the wetting and film formation of liquid mold release agents, the surface active substance (surfactants, emulsifiers) and defoamers are often used. Especially in the case of water-based release agents, stabilizers, for example, preservatives, and corrosion protectors should be used. Examples of such release agents can be found in different patents (EP 0 585 128 B1, DE 100 05 187 C2, JP 2001-259787 A, US 5,378,270). US 6,460,602 claims a process for producing magnesium components, where, for example, BN is applied in combination with soaps or waxes, and also water or oils, to surfaces of pressure casting molds, the intention of which is to increase in a different way the life time of the molds. The BN coating reduces the corrosion of the mold steel by the liquid metal. However, the release agent must be applied again after 10 impacts in each case. This allows the life times of the molds to increase clearly, since the use of BN is intended to clearly reduce the corrosive attack of magnesium. The application of liquid mold release agents suffers from problems, some of which are important. After each casting operation or after the removal of the casting, the wall of the hot mold is supplied at temperatures, for example, on the scale between 200-300 ° C with the release agent, preferably by spray application. Due to the hot surface of the die, there is a rapid evaporation of the solvent, as a result of which only some of the sprayed release agents (Leidenfrost phenomenon) remain on the surface. With the entry of the molten metal materials, generally at hundreds of degrees Celsius, the organic fraction of the release agents is thermally decomposed and forms a gas buffer between the die wall and the casting metal. Although this gas absorber leads to a desired elongation of the casting paths through the insulating action, this dissolves large amounts of gas in the workpiece. These dissolved gases can lead to the formation of pores and thus to an adverse influence on the mechanical properties of the casting. In the case of aluminum, the dissolved gases clearly worsen the welding properties or prevent the adaptability for welding. To solve these problems, one solution has been to evacuate the moles before loading with the molten metal materials and secondly to constantly increase the pressure during the course of the pressure casting (150 MPa). In addition, the fraction of the thermally unfoldable constituents in the release agent was reduced whenever possible. Although the use of vacuum (evacuation of the die cavity) before the casting process reduces the amount of gas incorporated in the casting, total prevention is not possible. The increase in pressure during the course of the formation leads to a reduction in the pores of gas but its internal pressure thus increases and a blister test (hardening by hot rest) can result in the formation of expanded regions in the surface of castings. Cyclic stresses on the surface of the mold by the application of sizes preferably comprises water as a solvent which further greatly increases the risk of formation of combustion fissures and thus restricts the life of the molds. In addition, the cyclic application results in considerable contamination of the environment, and, the exposure of personnel to the unused fraction of the release agent and also the decomposition products of the organic fractions. The reduction in thermally unfoldable fractions by the use of inorganic release agents have the advantage that they do not decompose under the action of high temperatures, but these release agents, in the case of incorporation into the work piece, can lead to an adverse influence on the surface properties of the casting, for example, discolorations, deterioration of the wettability or coating capacity, or defects in the interior of the casting. The use of inorganic release agents becomes problematic in the event of incomplete decomposition of the organic fractions, which can then lead to firmly adhering the cooked material to die surfaces. Especially in the case of production of complex thin walled components, this baked material is inconvenient. The use of release agents in dry particles, as described in DE 39 17 726 or US 6,291, 407, covers the development of specific application technology in order to ensure thin homogenous layers in the interiors of the complex mold, such as it is described in patents US 5,662,156, US 5,076,339, DE 100 41 309 or DE 4313961 C2. These release agents adhere to the metallic die surfaces by the use of fused organic components with high melting point in these particulate release agents, for example waxes or polymers which in turn thermally decompose in contact with casting metal. . The dry release agents in this manner must be applied again after each impact or casting procedure. A solution to the above problems arises from the binding of inorganic release agents, for example boron nitride, graphite, mica, talc, silicon nitride, molybdenum sulphide, Zr 2, AI 2 O 3, in a durable and technically stable manner to the surfaces of mold walls. One means for applying durable release layers to steels is that of the surface finishing process such as the CVD and PVD processes that are used to produce hard substance layers. In the CVD process, however, comparatively high substrate temperatures are necessary, which at at least 900 ° C are clearly above the temperatures of the molding steels. In the PVD process, clearly lower temperatures of 300-500 ° C are required. By means of specific plasma processes, the layers of TiN, TiC and TiB / TiN have been obtained in pressure casting molds. Some of the layers have very high hardness (HK0.005 325-3300). The lifetime of the molds is greatly increased by the factor of 30-80 and the use of the release agents is reduced by 97% to about 1% in the sizing. (Rie, Gebauer, Pfohl, Galvanotechnik 89, 1998 No. 10 3380-3388). It was not possible to completely dispense with the release agent. However, these coating processes are not trivial particularly for complex large volume molds (molds), since they require great experience and a high level of complexity in the apparatus. The molds are preferably coated in an external coating company after a complicated cleaning. An additional means for producing durable release layers is described in the international patent application WO 2000/056481. In this case, impervious and / or porous ceramic release layers with thicknesses of 250-400 μm are applied by means of thermal spray to mold surfaces. The inorganic release agents preferably have very high melting points and can therefore not be sintered with the generally metallic mold material due to the high temperatures necessary for this purpose. In order to fix the inorganic release agents to the generally metallic mold walls, therefore, high temperature, thermally stable and corrosion resistant joining phases are necessary.

For the precision casting of iron or steels, the release agents used are, for example, mixtures of Zr? 2 or Zr? 2 / Al2? 3. For CaO stabilized Zr? 2 release layers on ceramic substrates, graphite crucibles and metals, etc., an alkali metal silicate is specified as a binder. In this case also, the binder content is only a little percent based on the fraction of the inorganic release agent. For the production of glass products, for the protection of metal molds in accordance with US 4,039,377, mixtures of graphite / BN with combinations of water soluble and phosphatic silicic binders are used. This produces release layers with thicknesses of up to 2 millimeters. The recently published patent US Pat. No. 6,409,813 describes, for the continuous production of glass, stripping layers of BN with an oxidic fraction of 65-95% by weight and also a fraction of BN of 5-35%, in each case after calcination, with binders based on AI2O3 or Zr? 2, stabilized, which gives rise to impermeable layers on metal substrates at temperatures of at least 500 to 550 ° C, where the BN is completely surrounded by the oxidic phase. The oxidic phase of the binder is produced by means of precipitations of salts or alkoxides. The BN particles must be less than 5 μm. That is, it must increase the life times of the dice and metal molds considerably. US 6,051, 058 describes the production of protective layers of BN with thicknesses of 0.2 to 0.7 mm in refractory materials for the continuous casting of steels. In this case, BN with 20-50% by weight is bonded to the refractory material with the aid of high-temperature binders in the form of an aqueous coating solution based on the metal oxides of the Zr 2 groups, zirconium silicates, Al 2 O 3 , SÍO2 and aluminum phosphates. German patent application DE 196 47 36 A1 describes a process for producing thermally stable mixed materials with a silicic high temperature binder phase. This binder phase allows the production of mixed material of thermally stable material. In one example, the core sand for casting purposes is bonded by the silicic binder. In another example of this patent, a thermally stable molding was produced from a mixed material composed of 85% by weight of BN and 15% by weight of a binder phase consisting of a silicic binder phase and also ZrÜ2 nanodisperse fractions. Although, for example, the temperatures used in aluminum pressure casting are below the Si02 transformation scale, and although the binder has a higher shrinkage in compaction of these layers, these binders achieved layers of BN that, in addition to The adhesion to the substrate also has a certain anti-adhesive action against the cast metal, but the binders described in DE 196 47 368 A1 can not reliably prevent the penetration of the molten metal material into the layer, especially in the case of casting Pressure. It has been found that although the boron nitride cores are bonded together with this binder and thus the adhesion and the substrate are formed, as a result of which the mechanical properties are achieved which already support the standard pressure casting. , however, the cores are not completely coated and their anti-adhesive action is retained. Although DE 196 47 368 A1 includes the information that boron nitride can be bound with the binders described herein, as already mentioned, it is not possible with the formulations described here, as demonstrated by local investigations, to obtain a layer in molds of pressure casting that is stable to pressure casting. This is because these layers do not have sufficient adhesion of the BN particles in the layer or metal surface. In addition, these layers still have excessively high porosities and relatively rough surfaces that lead, in the case of pressurization of the molten metallic material, to infiltration in the surface and in this way the connection in fit form between the release layer and the casting, which in turn leads to the destruction of the release layer in the removal of the casting. Despite an increase in the binder content this leads to an improvement in the adhesion and reduction in the porosity with simultaneously high deterioration in the wetting behavior, so that the aluminum adheres strongly to the layer in wetting and corrosion experiments and can only be removed again in a forced manner with the destruction of the release layer. Thus, it is an object of the present invention to provide durable mold release layers with inorganic release agents for pressure casting of non-ferrous metals, which ensure smooth, relatively impervious mold release layers with high adhesion strength and Cutting resistance (adhesion to the mold and cohesion with each other) in the die-casting molds, usually made of steel, which are not wetted by the particular metallic fused materials, which do not have any corrosion as a result of the liquid metal, which have lubricating properties instead of durable fixation in case of complex mold geometries, which is not applied cyclically after each forming procedure but only at a certain predefined moment (number of impacts), which allows repair of local damage of the detachment layers, which can applied by means of common coating techniques (aspers ion, immersion, brushing, rolling, knife cutting, spin coating), which do not release any additional gaseous decomposition products after thermal compaction, which are thermally fixed or compacted at temperatures below 600 ° C and possibly obtained by metal fusion by itself (in situ), and their organic fractions necessarily present do not constitute any major contamination of the environment in relation to the amount and level of damage in the course of the application and subsequent thermal compaction. Surprisingly, this objective has been achieved by using refractory nanoscale binders as a binder phase for boron nitride.

The invention provides a sizing for producing a mold release layer with long-term stability, comprising: A) an inorganic binder comprising colloidal inorganic particles based on silicon oxide, zirconium oxide, or aluminum oxide or boehmite or mixtures thereof, additional inorganic fillers selected from the group comprising, Sio2, TiO2, ZrO2, AI2O3, AIOOH, Y2O3, CeO2, Sn02, iron and carbon oxides, and also optionally additional additives, wherein i) in the case of a binder comprising colloidal inorganic particles based on a silicon oxide, the binder further comprises one or more silanes of the general formula (1): R -Si-a4-x wherein A are each independently hydrolytically removable groups selected from group comprising hydrogen, halogens, hydroxyl groups, and alkoxy groups substituted or unsubstituted with 2 to 20 carbon atoms, aryloxy groups have from 6 to 22 carbon atoms, alkylaryloxy, acyloxy and alkylcarbonyl groups, R are each independently hydrolytically non-removable groups selected from the group comprising alkyl groups having 1 to 20 carbon atoms, alkenyl groups having 2 to 20 carbon atoms, alkynyl groups having 2 to 20 carbon atoms, aryl groups having 6 to 22 carbon atoms, alkaryl and arylalkyl groups, x is O, 1 , 2, 3, with the proviso that x > 1 for at least 50% of the amount of silanes, and substoichiometric amounts of water based on the hydrolysable groups of the silane component and optionally an organic solvent or ii) in the case of a binder free of inorganic particles colorations with an oxide base of silicon, the binder further comprises water as a solvent and, under the conditions of the sol-gel process, if appropriate with hydrolysis and condensation, forms a liquid colloid of a mixed nanobody, B) a suspension of boron nitride particles in the organic solvent in case the binder (i) is used, or in water in case the binder (ii) is used, and C) an organic solvent in case of that the binder (i) is used, or water in case the binder (ii) is used. The binders present in the sizes of the invention have surprisingly shown that they can bind boron nitride particles to give a fixed impermeable layer which does not infiltrate the metallic melt material and which does not reduce the anti-adhesion activity of the nitride cores of the metal. boron. It has been found that the useful binders are nanoscale SIO2 in conjunction with a specific surface modification, as described in the patent family for German specification DE 196 47 368 A1, whose content of the description in this matter forms a part of the application of this. The optimal dispersion of the BN particles, the partial replacement of the silane components, the use of additional inorganic fillers in the μm scale and the controlled adjustment of the pH of the sizing as a ready-to-apply coating system consists of an agent of detachment and binder that surprisingly allow to achieve the underlying objective. The invention further provides a process for producing a size to produce a mold release layer with long term stability and comprising A) an inorganic binder comprising inorganic colloidal particles based on silicon oxide, zirconium oxide or oxide of aluminum or boehmite or mixtures thereof, additional inorganic fillers selected from the group comprising SiO 2, TiO 2, Zr 2, Al 203, AlOOH, Y 2 O 3, CeO 2, Sn 2, oxides of iron and carbon, and also optionally additional additives, wherein i) in the case of a binder comprising colloidal inorganic particles based on silicon oxide, the binder further comprises one or more silanes of the general formula (1): Rx-Si-A4-X (1) wherein A are each independently hydrolytically removable groups selected from the group comprising hydrogen, halogens, hydroxyl groups and alkoxy groups substituted or unsubstituted by 2 to 20 carbon atoms, aryloxy groups with 6 to 22 carbon atoms, alkylaryloxy, acyloxy and alkylcarbonyl groups, R are each independently hydrolytically non-removable groups selected from the group comprises alkyl groups that have 1 to 20 carbon atoms, alkenyl groups having 2 to 20 carbon atoms, alkynyl groups with 2 to 20 carbon atoms, aryl groups with 6 to 22 carbon atoms, alkaryl and arylalkyl groups, x is 0, 1, 2, 3, with the proviso that x > 1 for at least 50% of the amount of silanes and. the substoichiometric amounts of water based on the hydrolysable groups of the silane component and optionally an organic solvent or i) in the case of a binder free of colloidal inorganic particles based on silicon oxide, the binder further comprises water as a solvent , and, under the conditions of the sol-gel process, if appropriate with hydrolysis or condensation, forms a liquid colloid of mixed nanobody, B) a suspension of boron nitride particles in the organic solvent in case the binder (i) ) is used, or in water in case the binder (ii) is used, and C) an organic solvent in case the binder (i) is used, or water in case the binder (i) is use, characterized in that the boron nitride is dispersed in the solvent and mixed with the inorganic binder. A preferred embodiment is a process for optimally dispersing the boron nitride powders, with which the BN particles are present in the form of dispersed platelets and the resulting or sizing suspensions have minimal viscosities. It is important that the dispersion of the particles is also maintained in the size comprising the binder. Optimal dispersion can be obtained surprisingly by the use of organic polymers such as polyvinyl butyrals or polyacrylic acids in the case of alcoholic solvents, or polyvinyl alcohols or polyvinylpyrrolidone in the case of water as a solvent, in combination with a high-performance centrifugal homogenizer as a solvent. dispersion unit. For durable fixation and simultaneously good dispersion, controlled adjustment of the pH of the sizing is also necessary, since the pH of the binder phase resulting from the synthesis is approximately in the order of magnitude of the isoelectric point of BN and leads to a precipitation premature of BN. Surprisingly, it is possible on a pH scale of about 3-4 to first obtain good fixation (hydrolysis / condensation) and secondly sufficient dispersion / stability of the BN particles. A different increase in the temperature of application or delayed fixation in the substrate can be achieved by partial replacement of a silane component (methyltriethoxysilane) by a phenyltriethoxysilane. This allows the application of mold-impervious release layers with increased surface temperatures of more than 80 ° C, which is impossible with the system based on DE 196 47 368. The organic fractions present preferably do not constitute any major contamination of the environment in relation with the quantity and level of danger in the course of the application and the subsequent thermal compaction; after thermal compaction, no additional gas decomposition product is released. The temperature for the necessary thermal fixation or compaction of the mold release layer with long-term stability is less than 600 ° C, that is, below the tempering temperature and may under some circumstances still be obtained by virtue of the molten metal by themselves (in situ). It was also possible to obtain, by means of common coating techniques (spraying, dipping, brushing, rolling, knife cutting, spin coating), comparatively impermeable and smooth release layers on a scale of 1 to 50 μm thickness that Instead they are not wetted by aluminum and, after aging in liquid aluminum at 750 ° C for several hours, they do not have any corrosion damage. In addition, it was possible to increase the strength of the layer to such an extent that the 0-1 classification was obtained in the trim test (DIN ISO 2409), and no damage to the layer was observed in the subsequent multiple tape test. In the Taber test (DIN 52347), although these layers did not present wear that arises linearly with an increased cycle number of 3.6 milligrams per 100 cycles, the layers based on DE 196 47 368, in contrast, were not tested by this method with the same BN to binder ratio due to too low resistances and related wear. The present invention further provides a mold release layer with long-term stability, characterized in that it is obtained from a size comprising A) an inorganic binder comprising inorganic colloidal particles based on silicon oxide, zirconium oxide or oxide of aluminum or boehmite or mixtures thereof, additional inorganic fillers selected from the group comprising SiO2, TiO2, Zr? 2, AI2O3, AIOOH, Y2O3, Ce02, Sn02, iron and carbon oxides, and also optionally additional additives, wherein i) in the case of a binder comprising colloidal inorganic particles based on silicon oxide, the binder further comprises one or more silanes of the general formula (1): Rx-Si-A4-X (1) wherein A are each independently hydrolytically removable groups selected from the group comprising hydrogen, halogens, hydroxy groups and alkoxy groups substituted or unsubstituted by 2 to 20 carbon atoms, aryloxy groups with 6 to 22 carbon atoms, alkylaryloxy, acyloxy groups and alkylcarbonyl, R each are independently hydrolytically non-removable groups selected from the group comprising alkyl groups with 1 to 20 carbon atoms, alkenyl groups with 2 to 20 carbon atoms, alkynyl groups with 2 to 20 carbon atoms, aryl groups with 6 to 22 carbon atoms, alkaryl and arylalkyl groups, X is 0, 1, 2, 3, with the proviso that X > 1 for at least 50% of the amount of silanes, and substoichiometric amounts of water based on the hydrolysable groups of the silane component and optionally an organic solvent ii) in the case of a binder free of colloidal inorganic particles based on the oxide of silicon, the binder further comprises water as a solvent and, under the conditions of the sol-gel process, if appropriate with hydrolysis and condensation, forms a liquid colloid of a mixed nanocupene, B) a suspension of boron nitride particles in the organic solvent in case the binder (i) is used, or in water in case the binder (ii) is used, and C) an organic solvent in case of that the binder (i) is used, or water in case the binder (ii) is used. The mold release layers of the invention allow use in the pressure casting scale, cycle numbers of more than 30 impacts are also possible. For repair purposes, this mold release layer system can be applied and compacted at locally restricted sites in an already measured mold, for example, by means of an airbrush technology or brushes, without significant loss in the properties to be observed. The total removal of the separation layer from the mold by means of a coating removal unit C02 in the same way is possible. The invention further provides a method for producing the mold release layer of the invention with long-term stability, characterized in that the size of the invention is applied to a firmly adherent layer on the metal surfaces. The process according to the invention preferably binds hexagonal boron nitride by means of the inventive binder in a thermally stable and durable manner for molding surfaces, for example metals, non-alloyed, low alloy or high alloy steels, copper or brass. The BN of the release agent preferably has average particle diameter of less than 100 μm, preferably less than 30 μm, more preferably less than 10 μm, and preferably greater than 0.1 μm, more preferably greater than 1 μm. The specific surface area, measured by the BET method, is preferably greater than 1 m2 / g and more preferably greater than 5 m2 / g. The BN used can contain up to 10% by weight of different impurities and additives. Particular mention should be made of boric acid, boron trioxide, carbon, alkali metal or earth alkali metal borates. However, preference is given to using BN washed with high purity with a purity of at least 98%, preferably 99%. In particular, preference is given to particle sizes of 2 to 3 μm. The boron nitride preferably has a crystal structure similar to hexagonal graphite. It is more preferred when the boron nitride is present in a deagglomerated form in the size. Based on the aforementioned components of the mold release layer, with long-term stability, the solids content of the inorganic binder is preferably between 5 and 95% by weight, preferably 20 to 80% by weight and more preferably between 30 and 70% by weight. Specific examples of inorganic fillers are liquid colloids and nanoscale powders which preferably have a particle diameter of less than 300 nm, preferably less than 100 nm and more preferably less than 50 nm of SiO2, TiO2, Zr0, Al203, AIOOH, Y2O3, Ce ? 2, Sn? 2, iron oxides, carbon (carbon free, graphite); Preference is given to Si02, Ti02, Zr02, Y-Zr02, Al203 and AIOOH. Particular preference is given to nanoparticles which preferably have a particle diameter of less than 300 nm, preferably less than 100 nm and more preferably less than 50 nm, of silicon oxide or zirconium oxides or mixtures thereof. Examples of the hydrolysable groups A mentioned in the formula (1) are hydrogen, halogens (F, Cl, Br and I), alkoxy groups (for example, ethoxy, i-propoxy, n-propoxy and butoxy), aryloxy groups, ( for example phenoxy), alkylaryloxy groups (for example, benzyloxy group), acyloxy groups (for example acetoxy, propionyloxy groups) and alkylcarbonyl groups (for example, acetyl group). Particularly preferred radicals are C2 alkoxy groups. 4 especially ethoxy groups. The non-removable hydrolytically radicals R are selected predominantly from the group comprising alkyl radicals (C 1. 4 alkyl such as methyl, propyl, and butyl radical), alkenyl radical (C 4 -alkenyl such as vinyl, 1-propenyl radical, 2). -propenyl and butenyl), alkynyl, aryl, alkaryl and arylalkyl radicals. Particularly preferred radicals are alkyl groups of C-i. 4 optionally substituted, especially methyl or ethyl groups, and optionally substituted aryl groups of CT-IO, especially phenyl group. The radicals A and R each can independently have one or more customary substituents, for example halogen, alkoxy, hydroxy, amino and epoxy groups. It is further preferred that, in the above formula (1), x have the value of 0, 1 or 2 and more preferably the value of 0 or 1. In addition, preferably at least 60% and in particular at least 70% of the quantity have the value x = 1. The binder phase at high inventive temperature can be produced, for example, from pure methyltriethoxysilane (MTEOS) or mixtures of MTEOS and tetraethoxysilane (TEOS) or MTEOS and phenyltriethoxysilane (PTEOS) and TEOS. The silanes of the general formula (1) used according to the invention can be used in whole or in part in the form of precondensates, that is to say compounds which have been formed by partial hydrolysis of the silanes of the formula (1) alone or in a mixture with other hydrolyzable compounds. Said oligomers preferably soluble in the reaction mixture can be partial condensates of low molecular weight of straight chain or cyclic, with a degree of condensation for example of about 2 to 100, in particular of 2 to 6. The amount of water used for hydrolysis and condensation is preferably 0.1 to 0.9 moles and preferably 0.25 to 0.8 moles of water per mole of hydrolysable groups present. The hydrolysis and condensation of the silicic binder phase is carried out under sol-gel conditions in the presence of acid condensation catalysts, preferably hydrochloric acid, at a pH of preferably between 1 and 7, preferably between 1 and 3. Preferably, an inventive preparation is obtained by optimal dispersion of the BN particles, the partial replacement of silane components, the use of an additional inorganic filler in the μm scale and by the addition of a certain amount of hydrochloric acid as a catalyst for a reaction of hydrolysis or controlled condensation, and also controlled adjustment of the pH of the sizes. The use of condensation catalysts leads to the mixture of silane / silica liquid colloid which may be present in biphasic form before becoming monophasic and, due to the hydrolysis or condensation reactions, the binding of the silanes to the Si02 particles or metallic substrate or boron nitride. Without the addition of HCl, often the result is a biphasic mixture in which the liquid colloid fraction of silica gels or precipitates. These investigations were carried out with commercial stabilized base silica liquid colloids and also stabilized with acid and always led to the same result.

In addition to the solvent which is formed in the hydrolysis, preference is given to not using any additional solvent, but if desired, it is possible to use water, alcoholic solvents (for example, ethanol) or other polar, protic and aprotic solvents (tetrahydrofuran, dioxane). When other solvents are to be used, preference is given to ethanol and 1-propanol, 2-propanol, ethylene glycol and derivatives thereof (for example, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether). To produce the binder, it is optionally possible to use other additives in amounts of up to 50% by weight, preferably less than 25% by weight, preferably less than 10% by weight, for example, curing catalysts such as metal salts, and alkoxides metal, dispersants and organic binders such as polyvinyl butyrals, polyethylene glycols, polyethylene imines, polyvinyl alcohols, polyvinyl pyrrolidones, pigments, dyes, oxidic particles, and also glass-forming components (for example, boric acid, boric esters, sodium ethoxide, potassium, aluminum sec-butoxide), corrosion protection and coating aids. Any additional inorganic filler may be selected from one or more of the classes of substances (SYNO2, AI2O3, ZR2, T02, mullite, boehmite, YES3, N, SiC, AIN, etc.). The particle diameters are usually less than 10 μm, preferably less than 5 μm and preferably less than 1 μm.

To produce colloidal inorganic particles based on Zr02 and AI2O3, the starting compounds used for the zirconium components may be, for example, one or more zirconium oxide precursors of the zirconium alkoxide substance classes, zirconium salts or compounds of zirconium forming complexes or colloidal ZrÜ2 particles which may be stabilized or not stabilized. The starting components for the aluminum components, for example, can be selected aluminum salts and aluminum alkoxides, or nanoscale AI2O3 or AIOOH particles in the form of liquid colloids or powders can be used. The solvents used to produce the binder phases based on Zr? 2 / Al2? 3, in addition to water, can also be aliphatic and alicyclic alcohols having from 1 to 8 carbon atoms (in particular, methanol, ethanol, n- i-propanol, butanol), aliphatic and alicyclic ketones (in particular acetone, butanone) having from 1 to 8 carbon atoms, esters (in particular, ethyl acetate), ethers, for example diethyl ether, dibutyl ether, anisole, dioxane , tetrahydrofuran, glycol ethers such as mono-, di-, tri- and polyglycol ether, glycols, such as ethylene glycol, diethylene glycol and polypropylene glycol, or other polar, protic and aprotic solvents. It will be appreciated that it is also possible to use mixtures of said solvents. In addition to water, preference is given to aliphatic alcohols (for example, ethanol, 1-propanol, 2-propanol) and also ethylene glycol and its derivatives (in particular, ethers, for example, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether).

Any additional inorganic filler can be added at several different times. For example, these fillers can be incorporated during the production of the BN suspension, but they can also be added to the binder in the form of powders or suspensions. To stabilize the oxidic particles in the liquid phase, it is possible, in addition to the inorganic and organic acids, to use modifiers which contain anhydride groups, acid amide groups, amino groups, SiOH groups, hydrolysable silane radicals, and also β-compounds -dicarbonyl. Particular preference is given to monocarboxylic acids having from 1 to 24 carbon atoms, for example formic acid, acetic acid, propionic acid, butyl acid, hexanoic acid, methacrylic acid, citric acid, stearic acid, methoxyacetic acid, dioxaheptanoic acid, acid 3, 6,9-trioxadecanoic, and also the corresponding acid hydrides and acid amides. The preferred β-dicarbonyl compounds are those having from 4 to 12 carbon atoms, in particular having 5-8 carbon atoms, for example diketones, such as acetylacetone, 2,4-hexanedione, acetoacetic acid, alkyl acetoacetates of C- such as ethyl acetoacetate. To disperse the oxidic powder particles in the binder phase, it is possible, in addition to the usual stirring units (dissolvers, directed jet mixers), to use ultrasound treatment, kneaders, screw extruders, roller mills, vibratory mills, planetary mills , mortar mills, and in particular wear mills. For the dispersion of the nanoscale powders, preference is given to attrition mills with small grinding bodies, usually less than 2 mm, preferably less than 1 mm and particularly less than 0.5 mm in diameter. The invention further provides a process for producing a suspension comprising boron nitride particles, characterized in that the boron nitride particles are suspended in an organic solvent with the addition of polyvinyl butyral or a polyacrylic acid or in water with the addition of a polyvinyl alcohol or polyvinylpyrrolidone. To produce BN suspensions, preference is given to dispersion with high speed dispersion units with rotor / stator systems, such as Ultra-Turrax homogenizers or centrifuges. Particular preference is given to units with multi-stage rotor / stator systems (Cavitron high performance centrifugal homogenizer). The inorganic release agent can be added by mixing BN suspensions and separate binders, but it can also be done by incorporating or dispersing the BN particles in the binder. Preference is given to the preparation by mixing separate BN suspensions with separate binder with agitation.

It is convenient, in some cases, before the application of the sizes, to adjust the pH of the binder or sizing. For this purpose, a base is usually used, preferably a base in an alcohol solvent and preferably an ethanolic solution of sodium ethoxide. The pH is usually adjusted between 1 and 7, preferably between 2.5 and 5 and particularly between 3 and 4. The salts formed in the course of the reaction can be removed by sedimentation or centrifugation. When finishing the sizing, it is convenient in some cases to homogenize the sizing before application. This is preferably done by stirring the sizing overnight. In some cases, it is also advantageous, through additions of exact amounts of water, to allow a hydrolysis or condensation reaction defined in the finished sizing; it is preferred to set a total water content of less than 1 mole of water per mole of hydrolyzable alkoxide group. Suitable substrates for the inventive mold release layers are a wide variety of different inorganic materials. Particularly suitable substrate materials are metallic materials such as iron, chromium, copper, nickel, aluminum, titanium, tin and zinc and alloys thereof, for example, cast iron, cast steel, steels, bronzes or brass and also non-metals inorganic materials such as ceramics, refractory materials and glass in the form of films, fabrics, sheets, plates or moldings. Liquid coating colloids containing the release agent can be applied to the substrate / mold surfaces by common coating methods such as knife coating, dipping, flow coating, spin coating, spraying, brushing and dispersion. In order to improve the adhesion, it is advantageous in some cases to treat the substrate before contact with liquid colloids of dilute or undiluted binder or precursors thereof or other initiators. The mold release agent preferably covers the entire surface of the pressure casting molds which are in contact with the molten or partially molten metal. The solids content of the sizing can be adjusted depending on the coating method selected by adding solvent or water. For spray coating, a solids content between 2 and 70% by weight, preferably between 5 and 50% by weight, preferably between 10 and 30% by weight, is usually established. For other coating methods, it is also possible to establish another solids content. It is also possible to add thixotropic or standardizing agents, for example cellulose derivatives. Isostatic compaction of newly applied release layers prior to final cure may further increase packing density and also distinctively increase the strength and lifetime of the layer. For this purpose, the application of another BN release layer virtually free of binder is recommended, which prevents the adhesion of the layer that has not yet been cured with the surrounding medium in isostatic compaction. The final cure may be preceded by one or more drying steps at room temperature or slightly elevated temperature, for example in a forced air drying cabinet, when heating or heat treating the mold itself. In the case of oxidation sensitive substrates, drying and / or subsequent curing can be carried out in a protective gas atmosphere, for example nitrogen or argon, or under reduced pressure. The thermal curing is preferably carried out by thermal treatment at temperatures above 50 ° C, preferably above 200 ° C and preferably above 300 ° C. The mold release layers can be treated with heat in a furnace, by hot gas, by direct gas flame of the mold surfaces, by direct or indirect IR heating or in situ by contacting the mold release layers with the molten, molten or partially molten metal. The thickness of the mold release layer cured in this way is preferably from 0.5 to 250 μm, preferably from 1 to 200 μm. Particularly preferably, a layer thickness of 5 to 20 μm is used for die-casting aluminum. The BN content of the cured mold release layer is preferably in the range of 20-80%, the rest in each case being formed by the inorganic binder comprising the nanoparticles.

EXAMPLES Synthesis of liquid colloids of silicic agglutinants: EXAMPLE 1 MTKS; ROR 0.4 65.5 g of MTEOS and 19.1 g of TEOS are mixed. Half of the mixture reacts with 14.2 g of liquid silica colloid (LEVASIL 300/30) and 0.4 ml of concentrated hydrochloric acid with vigorous stirring. After 5 minutes, the second half of the silane mixture is added to the mixture which is stirred for another 5 minutes. After resting overnight, the mixture is adjusted to a pH of 3 with ethanolic sodium ethoxide solution. The salts formed in the course of the reaction are removed by centrifugation.

EXAMPLE 2 MTZS; R0R 0.75 65.5 g of MTEOS and 19.1 g of TEOS are mixed. Half of the mixture reacts with 49.7 g of zirconium dioxide suspension with a solids content of 60% by weight (29.82 g of monoclinic Zr0 (INM, average particle size: about 8 nm) in 19.88 g of water) and 0.4 ml of concentrated hydrochloric acid with vigorous stirring. After 5 minutes, the second half of the silane mixture is added to the mixture which is stirred for another 5 minutes. After resting overnight, the mixture is stirred at a pH of 3 with ethanolic sodium ethoxide solution. The salts formed in the course of the reaction are removed by centrifugation.

EXAMPLE 3 MTKZS; R0R 0.75 A mixture of 16.4 g of MTEOS and 4.8 g of TEOS reacts with 14.2 g of Levasil 300/30 which had previously been adjusted to a pH of 7 with concentrated hydrochloric acid, and 0.2 ml of concentrated hydrochloric acid. In parallel, a mixture of 26.2 g of MTEOS and 7.7 g of TEOS reacts with 31.8 g of a suspension of 50% zirconium dioxide (15.9 g of monoclinic ZrO2 (INM, average particle size: about 8 nm) in 15.9 g of water) and 0.32 ml of concentrated hydrochloric acid. After 10 minutes, the two mixtures are combined. After another 5 minutes, the mixture combined with an additional silane mixture consisting of 42.6 g of MTEOS and 12.4 g of TEOS is added to the mixture and stirred for another 5 minutes. After resting overnight, the mixture is adjusted to a pH of 3 with ethanolic sodium ethoxide solution. The salts formed in the course of the reaction are removed by centrifugation.

EXAMPLE 4 MTKS-PT; ROR 0.4 65.5 g of MTEOS and 19.1 g of TEOS are mixed and reacted with 28.4 g of liquid silica colloid (LEVASIL 300/30) and 0.8 ml of concentrated hydrochloric acid with vigorous stirring. After 5 minutes, another silane mixture consisting of 88.3 g of phenyltriethoxysilane (PTOS) and 19.1 g of TEOS is added to the mixture which is stirred for another 5 minutes. After resting overnight, the mixture is adjusted to a pH of 3 with ethanolic sodium ethoxide solution. The salts formed in the course of the reaction are removed by centrifugation.

EXAMPLE 5 MTKS-PTTnP; R0R 0.4 65.5 g of MTEOS and 19.1 g of TEOS are mixed and reacted with 28.4 g of silica liquid colloid (LEVASIL 300/30) and 0.8 ml of concentrated hydrochloric acid with vigorous stirring. After 5 minutes, another silane mixture consisting of 88.3 g of phenyltriethoxysilane, 9.56 g of TEOS and 12.1 g of tetra-n-propoxysilane is added to the mixture which is stirred for another 5 minutes. After resting overnight, the mixture is adjusted to a pH of 3 with ethanolic sodium ethoxide solution. The salts formed in the course of the reaction are removed by centrifugation.

EXAMPLE 6 65. 5 g of MTEOS and 19.1 g of TEOS are mixed and reacted with 28.4 g of liquid silica colloid (LEVASIL 300/30) and 0.8 ml of concentrated hydrochloric acid with vigorous stirring. After 5 minutes, another silane mixture consisting of 88.3 g of phenyltriethoxysilane, 9.56 g of TEOS and 17.6 g of tetraethoxyethoxysilane is added to the mixture which is stirred for another 5 minutes. After resting overnight, the mixture is adjusted to a pH of 3 with ethanolic sodium ethoxide solution. The salts formed in the course of the reaction are removed by centrifugation.

Production of silicically bound BN layers: EXAMPLE 7 Preparation of ethanolic BN suspensions 0.8 kg of BN powder (BN E1; Wacker-Chemie GmbH, Munich) with a specific surface area, measured by the BET method of approximately 12 m2 / g and a purity of 99.0% are stirred in 1580 g of anhydrous, denatured ethanol (MEK) in which 20 g of polyvinyl butyral have been dissolved (Mowital B 30 T, Hoechst AG, Frankfurt). The suspension is charged to a chilled agitated vessel and dispersed with a high speed centrifugal rotor / stator homogenizer (Cavitron CD 1010) for a period of 60 minutes. After cooling to room temperature, the resulting suspension is diluted to a solids content of 30% by weight by adding 266.7 g of anhydrous, denatured ethanol.

EXAMPLE 8 Preparation of BN / MTKS sizing, mass ratio of BN: SiQ? = 2: 1 25 g of binder MTKS R0R 0.4 are activated with 1.25 g of demineralised water and stirred for 1 hour. Subsequently, 50 g of the ethanolic BN suspension of Example 7 with a solids content of 30% by weight are added to the binder with stirring. In order to adjust the solids content to 15% by weight, the suspension is diluted with 75 g of ethanol.

EXAMPLE 9 Preparation of BN / MTKS size, mass ratio of BN: SiO £ = 1: 1 50 g of MTKS ROR 0.4 binder are activated with 2.5 g of demineralised water and stirred for 1 hour. Subsequently, 50 g of the ethanolic BN suspension of Example 7 with a solids content of 30% by weight are added to the binder with stirring. The solids content of the sizing (based on BN) is 30% by weight. For a better processing capacity, the solids content can be diluted to 15% by weight by adding 100 g of anhydrous ethanol.

EXAMPLE 10 Preparing the sizes of BN / MTKZS, BN: (SiO? + N-ZrO?) = 2: 1 Ratio of mass of particles of n-Zr? 2: particles of SiO? = 20:80 21.4 g of binder MTKZS RO 0.75 are added with 50 g of the ethanolic BN suspension of example 7 with a solids content of 30% by weight with stirring. The solids content of the suspension can be diluted to 15% by weight by adding 78.6 g of ethanol.

EXAMPLE 11 Preparation of BN / MTKS-PT: BN: SiO? = 1: 1 50 g of MTKS-PT ROR 0.4 are activated with 2.5 g of demineralised water and stirred for 1 hour. Subsequently, the binder is added with 50 g of the ethanolic BN suspension of example 7 with a solids content of 30% by weight with stirring. The solids content of the sizing (based on BN) is 30% by weight; it can be reduced to 15% by weight by adding 100 g of anhydrous ethanol.

Preparation of the binder phase of A Og / ZrQ? EXAMPLE 12 NAnZ binder (1: 1) In order to prepare the binder phase, first 100 g of boehmite (Disperal from Sasol, Hamburg) are stirred in 900 g of water, and a constant pH of 3 is established in the course of gradually adding acetic acid. . The addition of acetic acid establishes a pH of 3. The suspension was stirred for 24 hours and the rough agglomerates were subsequently removed by sedimentation (48 h). 11.6 g of a Zr02 powder with modified surface, nanodisperse, stabilized with Y (INM: IZC4, specific surface areas of 200 g / cm3, 16% by weight of trioxadecanoic acid) are stirred in 128.37 g of the liquid colloid of boehmite (corresponding to 10 g of AI2O3) and dispersed by ultrasound treatment (Branson Sonifier) for a period of 30 minutes.

EXAMPLE 13 NAZ binder (1: 1) To prepare a liquid colloid of Zr 2, 36.86 g of Zr-n-propoxide in propanol (70% by weight) are mixed together with 16.89 g of acetic acid and 40.5 g of deionized water and Stir for 24 hours (molar ratio: 1: 2.5: 20). 9,425 g of this liquid colloid corresponds to 1 g of ZrO2. 28. 57 g of the liquid boehmite colloid of example 12 (corresponds to 2 g of Al203) and 18.85 g of the liquid colloid of Zr02 (corresponds to 2 g of Zr02) are mixed and stirred for 24 hours.

Production of BN layers joined with AI ?? ZrO? EXAMPLE 14 Preparation of an aqueous suspension of BN 1 kg of BET powder (BN E1, Wacker-Chemie GmbH, Munich) with a specific surface area, measured by the BET method, of approximately 12 m2 / g and a purity of 99.0% stir in 1950 g of deionized water in which 50 g of polyvinylpyrrolidone have been dissolved (PVP K-30, Hoechst AG, Frankfurt). The suspension is charged to a chilled agitated vessel and dispersed with a high speed roto / stator centrifugal homogenizer (Cavitron CD 1010) for a period of 30 min. The resulting suspension is diluted to a solids content of 20% by weight by adding 2 kg of demineralized H2O.

EXAMPLE 15 1 kg of BN powder (BN E1, Wacker-Chemie GmbH, Munich) with a specific surface area, measured by the BET method, of approximately 12 m2 / g and a purity of 99.0% is stirred in 1975 g of deionized water in which 25 g of polyvinyl alcohol have been dissolved (PVA 4/88, Hoechst AG, Frankfurt). The suspension is charged to a chilled agitated vessel and dispersed with a high speed rotor / stator centrifugal homogenizer (Cavitron CD 1010) for a period of 30 minutes. The resulting suspension is diluted to a solids content of 20% by weight by adding 2 kg of demineralized H2O.

EXAMPLE 16 Preparation of a BnAnZ sizing (2: 1: 1) To prepare the sizing, 30 g of the aqueous suspension of BN of Example 14, or alternatively of Example 15, (corresponding to 6 g of BN) are added dropwise to 41.99 g of the binder phase of nAnZ above. For better processing, a pH on the 4-6 scale can be established by adding aqueous ammonia. The sizing thus obtained can be applied to the substrates by means of common coating processes. After drying, the mold release layer can be thermally compacted / cured.

EXAMPLE 17 Preparation of BAnAnZ sizing In a first step, 80 g of Al203 (TM-DAR, from TAI MEI) in 318 g of HO and 2 g of acetic acid are dispersed at 70 revolutions / min in a wear mill (PE 075 of Netzsch) with 330 g of grinding spheres (AI2O3, diameter 4-5 mm) in a PE crushing vessel (+ rotor) for a period of 2 hours. To prepare the sizing, 35 g of the previous suspension of corundum (corresponds to: 7 g of AI2O3) are added first by dripping to 70 g of the binder liquid colloid nAnZ. 15 g of the aqueous suspension of BN of Example 14, or alternatively of Example 15, (corresponding to 3 g of BN) are added with stirring to this mixture. For better processing, a pH on the scale of approximately 4-6 can be established by adding aqueous ammonia, then the sizing can be used for coating by means of knife coating, casting or spraying.

EXAMPLE 18 Preparation of a BnAZ size 28.57 g of liquid colloid of boehmite (corresponding to 2 g of AI2O3) are stirred in 18.85 g of the liquid colloid of ZrO2. 30 g of the suspension of BN of Example 14, or alternatively of Example 15, (corresponding to 6 g of BN) are added to this mixture with stirring. A pH on the scale of about 4-5 can be established by adding aqueous ammonia, then sizing can be used for coating by knife coating, casting or spraying.

Claims (25)

NOVELTY OF THE INVENTION CLAIMS

1. - A size to produce a mold release layer with long term stability, comprising: A) an inorganic binder which comprises inorganic colloidal particles based on silicon oxide, zirconium oxide or aluminum oxide or boehmite or mixtures thereof, additional inorganic fillers selected from the group comprising SiO2, Ti02, ZrO2, AI2O3, AlOOH, Y2O3, CeO2, Sn02, iron and carbon oxides, and optionally other additives, wherein (i) in the case of a binder comprising colloidal inorganic particles based on silicon oxide, the binder further comprises one or more silanes of the general formula (1): wherein A are independently hydrolytically removable groups selected from the group comprising hydr, hals, hydroxyl groups and groups substituted or unsubstituted alkoxy having from 2 to 20 carbon atoms, aryloxy groups having from 6 to 22 carbon atoms, post alkylaryloxy, acyloxy and alkylcarbonyl, R are independently hydrolytically non-removable groups selected from the group comprising alkyl groups having from 1 to 20 carbon atoms, alkenyl groups having from 2 to 20 carbon atoms, alkynyl groups having from 2 to 20 carbon atoms, aryl groups having from 6 to 22 carbon atoms, alkaryl and arylalkyl groups, x is 0, 1, 2, 3, with the proviso that x > 1 for at least 50% of the amount of silanes, and substoichiometric amounts of water based on the hydrolysable groups of the silane component and optionally an organic solvent or ii) in the case of a binder free of inorganic colloidal particles based on silicon, the binder additionally comprises water as a solvent and, under the conditions of the sol-gel process, if convenient with hydrolysis and condensation, forms a liquid colloid of mixed nanobody, B) a suspension of boron nitride particles in the organic solvent in case the binder (i) is used, or in water in case the binder (ii) is used, and C) an organic solvent in case the binder (i) is used, or in water in case the binder is used (¡i).

2. The size according to claim 1, further characterized in that the polyvinyl butyral or a polyacrylic acid is added to the suspension of boron nitride particles in case the binder (i) is used, or an alcohol is added. polyvinyl or polyvinylpyrrolidone to the suspension in case the binder is used (ii).

3. The sizing according to claim 1 or 2, further characterized in that it has a pH of 3 to 4.

4. The sizing according to at least one of claims 1 to 3, further characterized in that the nitride of boron has a particle diameter of less than 10 μ and greater than 1 μm.

5. The size according to at least one of claims 1 to 4, further characterized in that the boron nitride has a hexagonal crystal structure similar to graphite.

6. The sizing according to at least one of claims 1 to 5, further characterized in that the boron nitride has a specific surface area measured by the BET method of 1 to 100 m2 / g.

7. The sizing according to at least one of claims 1 to 6, further characterized in that the boron nitride has a purity of at least 98%.

8. The sizing according to at least one of claims 1 to 7, further characterized in that the boron nitride is present in the size in deagglomerated form.

9. The sizing according to at least one of claims 1 to 8, further characterized in that the additional inorganic fillers are nanoparticles which preferably have a particle diameter of less than 300 nm, preferably less than 100 nm and preferably less than 50 nm, and are of silicon oxides or zirconium or boehmite oxides or mixtures thereof.

10. The sizing according to at least one of claims 1 to 9, further characterized in that the silanes used are methyltriethoxysilane, tetraethoxysilane or phenyltriethoxysilane or mixtures thereof.

11. - The sizing according to at least one of claims 1 to 10, further characterized in that the amount of water used for hydrolysis and condensation is 0.1 to 0.9 mol of water per mol of hydrolysable groups present.

12. The sizing according to at least one of claims 1 to 9, further characterized in that the starting compounds used for the zirconium components for the colloidal inorganic particles are one or more zirconium oxide precursors of the kinds of substances of zirconium alkoxides, zirconium salts or zirconium compounds that form complexes or colloidal Zr? 2 particles which may be stabilized or not stabilized.

13. The sizing according to at least one of claims 1 to 9 or 12, further characterized in that the starting compounds used for the aluminum components for the inorganic colloidal particles are aluminum salts, aluminum alkoxides, aluminum particles, AI2O3 or AlOOH nanoscale in the form of liquid colloids or powders.

14. A process for producing a size of at least one of claims 1 to 13, characterized in that boron nitride is dispersed in the solvent in a dispersion apparatus and mixed with the inorganic binder.

15. The process according to claim 14, further characterized in that polyvinyl butyral or a polyacrylic acid is added to the inorganic binder in case the binder (i) is used, or a polyvinyl alcohol or polyvinyl pyrrolidone is added to the inorganic binder in if the binder is used (ii).

16. The process according to claim 14 or 15, further characterized in that the dispersion apparatus used is a high-performance centrifugal homogenizer or Ultra-Turrax.

17. The process according to at least one of claims 14 to 16, further characterized in that the size has a pH of 3 to 4.

18.- A mold release layer with long-term stability, which can be obtain from a size of at least one of claims 1 to 13, characterized in that the layer thickness of the cured mold release layer is 0.5 to 250 μm.

19. The mold release layer according to claim 18, further characterized in that the temperature to fix or thermally compact the mold release layer is lower than 600 ° C.

20. The mold release layer according to claim 18, further characterized in that the mold release layer is obtained in situ by virtue of the metallic melt material.

21. The mold release layer according to at least one of claims 18 to 20, further characterized in that the BN content of the cured mold release layer is from 20 to 80% by weight.

22. - A method for producing a mold release layer with long-term stability of at least one of claims 18 to 21, characterized in that the size of at least one of claims 1 to 11 is applied to a firmly adherent layer on metallic or non-metallic inorganic surfaces.

23. The method according to claim 22, further characterized in that the metallic or non-metallic inorganic surfaces are iron, chromium, copper, nickel, aluminum, titanium, tin, zinc and alloys thereof, cast iron, cast steel, steels, bronzes, brass, ceramics, refractory materials and glass in the form of films, fabrics, sheets, plates or moldings.

24. The procedure according to claim 22 or 23, further characterized in that the sizing is applied to metallic or non-metallic inorganic surfaces by knife coating, dipping, flow coating, spin coating, spraying, brushing and dispersing.

25. A process for producing a suspension containing boron nitride particles, characterized in that the boron nitride particles are suspended in an organic solvent with the addition of polyvinyl butyral or a polyacrylic acid or in water with the addition of a polyvinyl alcohol or polyvinylpyrrolidone.