Use of Specially Coated Powdered Coating Materials and Coating Methods Using Such Coating Materials

Abstract

The present invention relates to the use of a particle-containing powdered coating material, wherein the surface of the particles is at least partially covered with a coating additive, in cold gas spraying, flame spraying, high-speed flame spraying, thermal plasma spraying and non-thermal plasma spraying. Furthermore, the present invention relates to coating methods, in particular the above-named methods, using the powdered coating material according to the invention.

Description

The present invention relates to the use of specially equipped powdered coating materials. Furthermore, the present invention comprises methods for substrate coating using specially equipped powdered coating materials. Furthermore, the present invention comprises powdered coating materials which are suitable for the above-named uses and/or methods.

A large number of coating methods for different substrates are already known. For example, metals or precursors thereof are deposited on a substrate surface from the gas phase, see e.g. PVD or CVD methods. Furthermore, corresponding substances can be deposited for example from a solution by means of galvanic methods. In addition, it is possible to apply coatings for example in the form of varnishes to the surface. However, all the methods have specific advantages and disadvantages. For example, in the case of deposition in the form of varnishes, large amounts of water and/or organic solvents are required, a drying time is needed, the coating material to be applied must be compatible with the base varnish, and a residue of the base varnish likewise remains on the substrate. For example, application by means of PVD methods requires large amounts of energy in order to bring non-volatile substances into the gas phase.

In view of the above-named limitations, a large number of coating methods have been developed to provide the properties desired for the respective intended use. Known methods use, for example, kinetic energy, thermal energy or mixtures thereof to produce the coatings, wherein the thermal energy can originate for example from a conventional combustion flame or a plasma flame. The latter are further divided into thermal and non-thermal plasmas, by which is meant that a gas has been partially or completely separated into free charge carriers such as ions or electrons.

In the case of cold gas spraying, the coating is formed by applying a powder to a substrate surface, wherein the powder particles are greatly accelerated. For this, a heated process gas is accelerated to ultrasonic speed by expansion in a de Laval nozzle and then the powder is injected. As a result of the high kinetic energy, the particles form a dense layer when they strike the substrate surface.

For example, WO 2010/003396 A1 discloses the use of cold gas spraying as a coating method for applying wear-protection coatings. Furthermore, disclosures of the cold gas spraying method are found for example in EP 1 363 811 A1, EP 0 911 425 B1 and U.S. Pat. No. 7,740,905 B2.

Flame spraying belongs to the group of thermal coating methods. Here, a powdered coating material is introduced into the flame of a fuel gas/oxygen mixture. Here, temperatures of up to approximately 3200° C. can be reached for example with oxyacetylene flames. Details of the method can be learned from publications such as e.g. EP 830 464 B1 and U.S. Pat. No. 5,207,382 A.

In the case of thermal plasma spraying, a powdered coating material is injected into a thermal plasma. In the typically used thermal plasma, temperatures of up to approx. 20,000 K are reached, whereby the injected powder is melted and deposited on a substrate as coating.

The method of thermal plasma spraying and specific embodiments, as well as method parameters are known to a person skilled in the art. By way of example, reference is made to WO 2004/016821, which describes the use of thermal plasma spraying to apply an amorphous coating. Furthermore, EP 0 344 781 for example discloses the use of flame spraying and thermal plasma spraying as coating methods using a tungsten carbide powder mixture. Specific devices for use in plasma spraying methods are described multiple times in the literature, such as for example in EP 0 342 428 A2, U.S. Pat. No. 7,678,428 B2, U.S. Pat. No. 7,928,338 B2 and EP 1 287 898 A2.

In the case of high-speed flame spraying, a fuel is combusted under high pressure, wherein fuel gases, liquid fuels and mixtures thereof can all be used as fuel. A powdered coating material is injected into the highly accelerated flame. This method is known for being characterized by relatively dense spray coatings.

High-speed flame spraying is also well known to a person skilled in the art and has already been described in numerous publications. For example, EP 0 825 272 A2 discloses a substrate coating with a copper alloy using high-speed flame spraying. Furthermore, WO 2010/037548 A1 and EP 0 492 384 A1 for example disclose the method of high-speed flame spraying and devices to be used therein.

Non-thermal plasma spraying is carried out largely analogously to thermal plasma spraying and flame spraying. A powdered coating material is injected into a non-thermal plasma and deposited with it onto a substrate surface. As can be learned for example from EP 1 675 971 B1, this method is characterized by a particularly low thermal load of the coated substrate. This method, particular embodiments and corresponding method parameters are also known to a person skilled in the art from various publications. For example, EP 2 104 750 A2 describes the use of this method and a device for carrying it out. For example, DE 103 20 379 A1 describes the production of an electrically heatable element using this method.

Further disclosures in respect of the method or devices for non-thermal plasma spraying are found for example in EP 1 675 971 B1, DE 10 2006 061 435 A1, WO 03/064061 A1, WO 2005/031026 A1, DE 198 07 086 A1, DE 101 16 502 A1, WO 01/32949 A1, EP 0 254 424 B1, EP 1 024 222 A2, DE 195 32 412 A1, DE 199 55 880 A1 and DE 198 56 307 01.

However, a particular problem of coating methods using a powdered coating material is that powdered coating materials form agglomerates which form a non-uniform coating when applied to the substrate surface.

An object of the present invention is to improve existing methods for substrate coating and to make possible novel methods for substrate coating. In particular the problems caused by agglomerates of the powdered coating material are to be minimized or eliminated by the present invention.

Furthermore, the production of particularly thin layers is to be made possible or simplified by the present invention.

Furthermore, the methods according to the invention are to make new coatings available and/or make it possible to produce known coatings of particularly high quality.

A further object of the present invention is to provide a powdered coating material which is particularly suitable for one of the above-named uses in coating methods.

The present invention relates to the use of a particle-containing powdered coating material, the surface of which is equipped with at least one coating additive which has a boiling point or decomposition temperature of below 500° C., in a coating method selected from the group consisting of cold gas spraying, flame spraying, high-speed flame spraying, thermal plasma spraying and non-thermal plasma spraying.

In particular embodiments of the above-named use, the weight proportion of the at least one coating additive is at least 0.01 wt.-%, relative to the total weight of the coating material and the coating additive.

In particular embodiments of the above-named uses, the weight proportion of the at least one coating additive is at most 80 wt.-%, relative to the total weight of the coating material and the coating additive.

In particular embodiments of the above-named uses, the particles of the powdered coating material comprise or are metal particles, wherein the metal is selected from the group consisting of silver, gold, platinum, palladium, vanadium, chromium, manganese, cobalt, germanium, antimony, aluminum, zinc, tin, iron, copper, nickel, titanium, silicon, alloys and mixtures thereof.

In particular embodiments of the above-named uses, the carbon content of the powdered coating material is from 0.01 wt.-% to 15 wt.-%, in each case relative to the total weight of the coating material and the coating additive.

In particular embodiments of the above-named uses, the compounds used as coating additive have at least 6 carbon atoms.

In particular embodiments of the above-named uses, the coating method is selected from the group consisting of flame spraying and non-thermal plasma spraying. In particular ones of the above-named embodiments, the coating method is preferably non-thermal plasma spraying.

In particular embodiments of the above-named uses, the at least one coating additive is selected from the group consisting of polymers, monomers, silanes, waxes, oxidized waxes, carboxylic acids, phosphonic acids, derivatives of the above-named and mixtures thereof.

In particular embodiments of the above-named uses, the at least one coating additive comprises no stearic acid and/or oleic acid and preferably no saturated or unsaturated C18 carboxylic acids, more preferably no saturated or unsaturated C14 to C18 carboxylic acids, still more preferably no saturated or unsaturated C12 to C18 carboxylic acids and most preferably no saturated or unsaturated C10 to C20 carboxylic acids.

In particular embodiments of the above-named uses, the coating additive was applied to the particles mechanically.

In particular embodiments of the above-named uses, the powdered coating material has a particle-size distribution with a D₅₀ value from a range of from 1.5 to 53 μm.

Furthermore, the present invention relates to methods for coating a substrate selected from the group consisting of cold gas spraying, flame spraying, high-speed flame spraying, thermal plasma spraying and non-thermal plasma spraying, in which a particle-containing powdered coating material is used, wherein the particles are equipped with at least one coating additive which has a boiling point or decomposition temperature of below 500° C.

In particular embodiments of the above-named methods, the method is selected from the group consisting of flame spraying and non-thermal plasma spraying. The coating method is preferably non-thermal plasma spraying.

In particular embodiments of the above-named methods, the powdered coating material is conveyed as an aerosol.

In particular embodiments of the above-named methods, the medium directed onto the substrate is air or has been produced from air.

The term “powdered coating material” within the meaning of the present invention relates to a particle mixture which is applied to the substrate as coating. The equipping of the surface of the particles of the powdered coating material according to the invention need not be unbroken here. Without being understood as limiting the invention, the inventors are of the view that even a small application to or a small coverage of the surface of the particles of the powdered coating material is sufficient to break up agglomerates under the conditions of the coating method. In particular, the inventors are of the view that, because of the large gas volume of the coating additive applied according to the invention to the particles or of its decomposition products, even small quantities of the coating additive are sufficient to break up any agglomerates present. The at least one coating additive according to the invention is here applied to the surface of the particles of the powdered coating material. In particular embodiments, it is preferred in particular that one (number: 1) coating additive is applied. This provides the advantage that variations in the properties of the powdered coating material according to the invention as a result of an incomplete mixing of the constituents of the coating additive before application to the particles are prevented. On the other hand, in other embodiments, it is preferred to use a mixture of at least two different substances as coating additive. This can, for example, make possible a simple adaptation of the properties of the powdered coating material according to the invention to different requirements. The substances used according to the invention as coating additive can, for example, be physically and/or chemically bound to the surface of the particles. Furthermore, the coating additive can completely or partially envelop the particles of the powdered coating material for example in the form of coatings.

It has surprisingly been established that, by applying a coating additive with a low boiling point or decomposition temperature to the surface of the particles of the powdered coating material during storage or following conveying, any agglomerates that have formed can be broken up in the course of the coating method and particularly high-quality coatings are obtained. Furthermore, the use of the powdered coating material according to the invention allows a more uniform coating, with the result that for example the production of particularly thin coatings is made possible.

Methods according to the invention which can be used to build up coatings are cold gas spraying, thermal plasma spraying, non-thermal plasma spraying, flame spraying and high-speed flame spraying. As evaporation or decomposition of the coating additive is necessary, however, the variants of cold gas spraying according to the invention are limited to embodiments in which a heated gas stream is used, with the result that sufficient thermal energy for the evaporation or decomposition of the coating additive is available. In particular embodiments of the present invention using cold gas spraying, it is preferred in particular that the temperature of the gas stream is at least 250° C., preferably at least 350° C., more preferably at least 450° C. and still more preferably at least 500° C.

As the high speeds of the gas streams in cold gas spraying and in high-speed flame spraying give rise to only a short residence time of the powdered coating material in the gas stream or the flame, it can be difficult in such methods to guarantee that the agglomerates break up in good time. In particular embodiments, it is therefore preferred that the method is selected from the group consisting of thermal plasma spraying, non-thermal plasma spraying and flame spraying.

As many coating materials are completely melted in the thermal plasma of the thermal plasma spraying and strike the surface of the substrate as a liquid, the additional outlay associated with the application of the coating additive according to the invention to the surface of the particles of the powdered coating material is uneconomical in particular cases, for example if no particularly uniform coating is to be achieved. In particular embodiments, the method is therefore selected from the group consisting of cold gas spraying, non-thermal plasma spraying, flame spraying and high-speed flame spraying, preferably from the group consisting of non-thermal plasma spraying and flame spraying.

The use of the plasma-based methods provides the advantage for example that even non-combustible gases can be used. This makes the industrial-scale storage of the gases used easier, as for example the requirements in terms of safety technology are reduced. Where air is used, the gas required can optionally even be taken directly from the atmosphere. In particular quite particularly preferred embodiments, the coating method is therefore selected from the group consisting of thermal plasma spraying and non-thermal plasma spraying. In particular ones of the above-named embodiments, it is preferred in particular that the method is non-thermal plasma spraying.

The coating additive applied according to the invention to the surface of the particles of the powdered coating material is characterized by the above-named upper limit of the boiling point or decomposition temperature. If the substance in question has both a boiling point and a decomposition temperature, only the lower temperature is considered. It is not strictly necessary here that a gas is released when the coating additive decomposes. Without being understood as limiting the invention, any agglomerates present also appear to disintegrate during decomposition without releasing a gas. The inventors are of the view that, due to the decomposition of the coating additive, its surface properties change and this change in turn leads to a disintegration of the agglomerates. In particular embodiments, however, it is preferred in particular that, during decomposition, the coating additive used releases a gas which forces open any agglomerates present. The boiling point or decomposition temperature can be determined by means of methods known to a person skilled in the art. For example, the decomposition temperature of polymers can be determined by means of thermogravimetry according to DIN EN ISO 11358.

The decomposition temperature or boiling point of the coating additive to be applied according to the invention to the surface of the particles lies below 500° C., preferably below 470° C., more preferably below 440° C. and still more preferably below 420° C. In particular embodiments, it is preferred in particular that the decomposition temperature or boiling point of the substances applied to the surface of the particles lies below 400° C., preferably below 380° C., more preferably below 360° C. and still more preferably below 340° C.

The coating additives applied to the surface of the particles according to the invention need not be bound to the surface of the particles. However, in particular embodiments, it is preferred that the coating additives according to the invention are chemically and/or physically bound to the surface of the particles. For example, in cases where the powder must be able to be subjected even to larger mechanical loads, it can be preferred that the coating additives are bound particularly securely to the surface of the particles. In particular embodiments, therefore, it is preferred that the coating additives are bound to the surface with at least one type of chemical bond. Examples of chemical bonds are covalent and ionic bonds. In further cases, where the coating additive must be able to be released again particularly easily, it can be preferred in contrast that the coating additives are bound to the surface of the particles only by means of physical bonds. In particular embodiments, therefore, it is preferred that the binding of the coating additives to the surface of the particles takes place only by means of physical bonds. Furthermore, it can be preferred that the coating additive forms a stable shell around the particles according to the invention, with the result that for example no physical or chemical bonds are necessary to hold the particles inside this shell. Without being understood as limiting the invention, the inventors are of the view that such a coating additive in the form of a stable shell without strong bonds to the particles can be released particularly easily, as the shell can already be released easily after a partial evaporation or decomposition. In particular embodiments, therefore, it is preferred that the coating additive forms a stable shell around the particles, wherein this shell does not have an opening that would be large enough for the particles to find their way out of the shell through it. The term “stable shell” within the meaning of the present invention describes that the coating additive forms a shell around the particles of the powdered coating material which is not destroyed under the conditions of storage and conveying.

The coating additives according to the invention can be applied to the particles by means of a wide variety of methods. For example, coatings of the particles can be obtained by polymerization of a monomer and/or from sol-gel processes. For example, stable shells consisting of the coating additive can be obtained here. Furthermore, the coating additives according to the invention can be applied to the surface of the particles for example by deposition from a supersaturated solution or by mechanical forces. Such methods are particularly suitable for applying coating additives to large quantities of powdered coating material in a simple and cost-effective manner.

Without being understood as limiting the present invention, the inventors are of the view that the use of coating additives with a high carbon content following the release of CO₂ makes possible a particularly good breakup of the agglomerates. In particular embodiments, therefore, it is preferred that the weight proportion of the carbon atoms in the powdered coating material according to the invention is at least 0.01 wt.-%, preferably at least 0.05 wt.-%, more preferably at least 0.1 wt.-% and still more preferably at least 0.17 wt.-%. In particular embodiments, it is preferred in particular that the weight proportion of the carbon atoms in the powdered coating material according to the invention is at least 0.22 wt.-%, preferably at least 0.28 wt.-%, more preferably at least 0.34 wt.-% and still more preferably at least 0.4 wt.-%. The above-named wt.-% are based on the total weight of the coating material according to the invention and the coating additive. The weight proportion of the carbon atoms to the total weight of the powdered coating material according to the invention is determined for example with a CS 200 device from Leco Instruments GmbH.

On the other hand, in particular embodiments, it is preferred that the weight proportion of the carbon atoms in the powdered coating material according to the invention is at most 15 wt.-%, preferably at most 10 wt.-%, more preferably at most 7 wt.-% and still more preferably at most 5 wt.-%. In particular ones of the above-named embodiments, it is preferred in particular that the carbon content is at most 4 wt.-%, preferably at most 3 wt.-%, more preferably at most 2 wt.-% and still more preferably at most 1 wt.-%. The above-named wt.-% are based on the total weight of the coating material according to the invention and the coating additive.

In particular embodiments, it is preferred in particular that the weight proportion of the carbon atoms in the powdered coating material according to the invention is from a range of between 0.01 wt.-% and 15 wt.-%, preferably from a range of between 0.05 wt.-% and 10 wt.-%, more preferably from a range of between 0.1 wt.-% and 7 wt.-% and still more preferably from a range of between 0.17 wt.-% and 5 wt.-%. In particular ones of the above-named embodiments, it is preferred in particular that the weight proportion of the carbon atoms in the powdered coating material according to the invention is from a range of between 0.22 wt.-% and 4 wt.-%, preferably from a range of between 0.28 wt.-% and 3 wt.-%, more preferably from a range of between 0.34 wt.-% and 2 wt.-% and still more preferably from a range of between 0.4 wt.-% and 1 wt.-%. The above-named wt.-% are based on the total weight of the coating material according to the invention and the coating additive.

In particular embodiments, furthermore, it is preferred that the compounds used as coating additive contain at least 6 carbon atoms, preferably at least 7 carbon atoms, more preferably at least 8 carbon atoms and still more preferably at least 9 carbon atoms. In particular ones of the above-named embodiments, it is preferred in particular that the compounds used as coating additive contain at least 10 carbon atoms, preferably at least 11 carbon atoms, more preferably at least 12 carbon atoms and still more preferably at least 13 carbon atoms. The number of carbon atoms contained in the coating additive according to the invention can be determined for example by determining the respective coating additive. All methods known to a person skilled in the art for determining a substance can be used here. For example, a coating additive can be removed from the particles of the powdered coating material using organic and/or aqueous solvents and then identified by means of HPLC, GCMS, NMR, CHN or combinations of the above-named with each other or with other routinely used methods.

In particular embodiments, it is preferred to apply only a small quantity of coating additive to the surface of the particles in order to prevent too strong a disruption of for example the plasma flame used for the coating by the formation of large quantities of gas. In particular embodiments of the present invention, therefore, it is preferred that the quantity of coating additive is at most 80 wt.-%, preferably at most 70 wt.-%, more preferably at most 65 wt.-% and still more preferably at most 62 wt.-%. In particular ones of the above-named embodiments, it is preferred in particular that the quantity of coating additive is at most 59 wt.-%, preferably at most 57 wt.-%, more preferably at most 55 wt.-% and still more preferably at most 53 wt.-%. The above-named wt.-% are based on the total weight of the coating material including the coating additive.

Furthermore, in particular embodiments using, for example, powdered coating materials which have a particularly strong tendency to form solid agglomerates, it can be advantageous to apply a minimum quantity of coating additive in order to ensure a breakup of the agglomerates. In particular embodiments, therefore, it is preferred that the quantity of coating additive is at least 0.02 wt.-%, preferably at least 0.08 wt.-%, more preferably at least 0.17 wt.-% and still more preferably at least 0.30 wt.-%. In particular ones of the above-named embodiments, it is preferred in particular that the quantity of coating additive is at least 0.35 wt.-%, preferably at least 0.42 wt.-%, more preferably at least 0.54 wt.-% and still more preferably at least 0.62 wt.-%. The above-named wt.-% are based on the total weight of the coating material including the coating additive.

In further particular embodiments, it is furthermore preferred that the weight proportion of the coating additive is from a range of between 0.02 wt.-% and 80 wt.-%, preferably from a range of between 0.08 wt.-% and 70 wt.-%, more preferably from a range of between 0.17 wt.-% and 65 wt.-% and still more preferably from a range of between 0.30 wt.-% and 62 wt.-%. In particular ones of the above-named embodiments, it is preferred in particular that the weight proportion of the carbon atoms in the powdered coating material according to the invention is from a range of between 0.35 wt.-% and 59 wt.-%, preferably from a range of between 0.42 wt.-% and 57 wt.-%, more preferably from a range of between 0.54 wt.-% and 55 wt.-% and still more preferably from a range of between 0.62 wt.-% and 53 wt.-%. The above-named wt.-% are based on the total weight of the coating material according to the invention including the coating additive.

Examples of substances which can be used as coating additives within the meaning of the present invention are:

polymers (e.g. polysaccharides, plastics), monomers, silanes, waxes, oxidized waxes, carboxylic acids (e.g. fatty acids), phosphonic acids, derivatives of the above-named (in particular carboxylic acid derivatives and phosphoric acid derivatives) and mixtures thereof. In particular embodiments, it is preferred that polysaccharides, plastics, silanes, waxes, oxidized waxes, carboxylic acids (e.g. fatty acids) carboxylic acid derivatives, phosphonic acids, phosphoric acid derivatives or mixtures thereof, preferably polysaccharides, silanes, waxes, oxidized waxes, carboxylic acids (e.g. fatty acids) carboxylic acid derivatives, phosphonic acids, phosphoric acid derivatives or mixtures thereof, more preferably polysaccharides, silanes, waxes, oxidized waxes, carboxylic acids (e.g. fatty acids), carboxylic acid derivatives, phosphonic acids, phosphoric acid derivatives or mixtures thereof, and still more preferably polysaccharides, silanes, waxes, oxidized waxes, phosphonic acids, phosphoric acid derivatives or mixtures thereof, are used as coating additive.

The above-named waxes comprise both natural waxes and synthetic waxes. Examples of such waxes are paraffin waxes, petroleum waxes, montan waxes, animal waxes (e.g. beeswax, shellac, wool wax), vegetable waxes (e.g. carnauba wax, candelilla wax, rice bran wax), fatty acid amide waxes (such as e.g. erucamide), polyolefin waxes (such as e.g. polyethylene waxes, polypropylene waxes), grafted polyolefin waxes, Fischer-Tropsch waxes, and oxidized polyethylene waxes and modified polyethylene and polypropylene waxes (e.g. metallocene waxes). The waxes according to the invention are bound only via physical bonds in particular preferred embodiments. However, it is not ruled out that in further particular embodiments the waxes have functional groups which alternatively or additionally make a chemical bond, in particular an ionic and/or covalent bond, possible.

The term “polymer” within the meaning of the present invention also comprises oligomers. In particular preferred embodiments, the polymers used according to the invention are, however, preferably built up of at least 25 monomer units, more preferably of at least 35 monomer units, still more preferably of at least 45 monomer units and most preferably of at least 50 monomer units. The polymers can be bound here to the particles of the powdered coating material without covalent or ionic bonds being formed. In particular embodiments, however, it is preferred that the coating additive according to the invention can form at least one ionic or covalent bond with the particles of the powdered coating material. In particular ones of the above-named embodiments, such a binding preferably takes place via a phosphoric acid, carboxylic acid, silane or sulfonic acid group contained in the polymer.

The term “polysaccharide” within the meaning of the present invention also comprises oligosaccharides. In particular preferred embodiments, the polysaccharides used according to the invention are, however, preferably built up of at least 4 monomer units, more preferably of at least 8 monomer units, still more preferably of at least 10 monomer units and most preferably of at least 12 monomer units. In particular embodiments, particularly preferred polysaccharides are cellulose, cellulose derivatives such as e.g. methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, nitrocellulose (e.g. ethocel, or methocel from Dow Wolff Cellulosics), cellulose esters (e.g. cellulose acetate, cellulose acetobutyrate, and cellulose propionate), starches such as e.g. corn starch, potato starch and wheat starch and modified starches.

The term “plastic” within the meaning of the present invention comprises thermoplastic, thermosetting or elastomeric plastics. Because of the possibility of adapting the properties of the plastics in a targeted manner, it is preferred in particular embodiments that the additive is a plastic. For example, for the production of resistant, in particular hard, coatings of the particles according to the invention, the use of elastomers and thermosetting plastics, in particular thermosetting plastics, can be preferred. In particular embodiments, the plastic used according to the invention is therefore an elastomer or thermosetting plastic, preferably a thermosetting plastic. Furthermore, a particularly simple application of the plastic for example by means of mechanical forces can be to the fore and the use of thermoplastics can be preferred. In particular embodiments, the plastic used according to the invention is therefore a thermoplastic. Corresponding plastics which are characterized by a corresponding decomposition temperature or boiling point are known to a person skilled in the art and are found for example in the Kunststoff-Taschenbuch, ed. Saechtling, 25th edition, Hanser-Verlag, Munich, 1992, as well as references cited therein, and in the Kunststoff-Handbuch, ed. G. Becker and D. Braun, volumes 1 to 11, Hanser-Verlag, Munich, 1966 to 1996. Without being limited to this, the following plastics are to be named by way of example for illustration: polycarbonates (PC), polyoxyalkylenes, polyolefins such as polyethylene or polypropylene (PP), polyarylene ethers such as polyphenylene ether (PPE), polysulfones, polyurethanes, polylactides, polyamides, vinylaromatic (co)polymers such as polystyrene, impact-modified polystyrene (such as HIPS) or ASA, ABS or AES polymers, halogen-containing polymers, polyesters such as polybutylene terephthalate (PBT) or polyethylene terephthalate (PET), polymers containing imide groups, cellulose esters, poly(meth)acrylates, silicone polymers and thermoplastic elastomers. Mixtures of different plastics, in particular different thermoplastics, can also be used in the form of single- or multi-phase polymer blends.

In particular embodiments, it is preferred that the coating method is not non-thermal plasma spraying if the additive is a plastic, in particular if the additive is a thermosetting plastic or elastomer. In particular ones of the above-named embodiments, it is preferred in particular that the coating method is not non-thermal plasma spraying if the additive is a thermosetting plastic.

The poly(meth)acrylates used according to the invention can be present as homopolymers or as block polymers. Examples are polymethyl methacrylate (PMMA) and copolymers based on methyl methacrylate with up to 40 wt.-% further copolymerizable monomers, such as e.g. n-butyl acrylate, t-butyl acrylate or 2-ethylhexyl acrylate.

In particular embodiments, particularly preferred plastic layers are synthetic resin layers of organofunctional silane and acrylate and/or methacrylate compound(s). Such coatings according to the invention of the particles of the powdered coating material additionally display a particular stability against mechanical shearing forces, in addition to the above-named advantages. Furthermore, such coatings protect, for example, metal pigments against chemicals, strongly aggressive and/or corrosive media.

The above-named synthetic resin layer can be relatively thin. For example, it can have an average layer thickness in a range of from 10 nm to 300 nm, preferably from 15 nm to 220 nm. In particular embodiments, the average layer thickness lies in a range of from 25 to 170 nm, more preferably in a range of from 35 to 145 nm.

The average layer thickness is determined by measuring the layer thicknesses of at least 30 randomly selected particles by means of SEM.

It is advantageously possible to apply such a synthetic resin layer to the particles according to the invention in a one-stage method, whereby the production costs are kept low. In particular preferred embodiments, the organofunctional silane here is in the polyacrylate and/or polymethacrylate before and/or is incorporated by polymerization.

Furthermore, it is preferred in particular embodiments that the plastic layer, in particular the synthetic resin layer, has no inorganic network. A pure and homogeneous plastic coating, and in particular a pure and homogeneous synthetic resin coating, has proved to be sufficient to provide the corrosion stability and chemicals stability necessary under the conditions to be expected of storage, preparation, etc. which precede a use in the one coating method. At the same time, the necessity to remove the inorganic network under the conditions of the coating method is avoided.

The above-named organofunctional silane contained in a synthetic resin layer has at least one functional group which can be reacted chemically with an acrylate group and/or methacrylate group of polyacrylate and/or polymethacrylate. Radically polymerizable organic functional groups have proved to be very suitable. Preferably, the at least one functional group is selected from the group which consists of acryl, methacryl, vinyl, allyl, ethinyl as well as further organic groups with unsaturated functions. Preferably, the organofunctional silane has at least one acrylate and/or methacrylate group, because these can be reacted with the acrylate or methacrylate compounds used to produce the polyacrylate and/or polymethacrylate completely problem-free, accompanied by the formation of a homogeneous plastic layer. The organofunctional silane can be present as a monomer or also as a polymer. It is important that the, monomeric or polymeric, organofunctional silane has at least one functional group which allows a chemical reaction with an acrylate and/or methacrylate group. Mixtures of different monomeric and/or polymeric organofunctional silanes can also be contained in the synthetic resin layer. For the production of particularly high-quality synthetic resin layers it has been shown that there must be a homogeneous mixing of the organofunctional silane with the polyacrylate and/or polymethacrylate. In contrast, it is not necessary here that the organofunctional silane is completely reacted chemically with the polyacrylate and/or polymethacrylate. The chemical reaction between organofunctional silane and polyacrylate and/or polymethacrylate can therefore be carried out only partially, with the result that for example only 30% or 40% of the organofunctional silane present, relative to the total weight of organofunctional silane, is reacted with polyacrylate and/or polymethacrylate. However, in particular embodiments, it is preferred that at least 60%, further preferably at least 70%, still further preferably at least 80% of the organofunctional silane present, in each case relative to the total weight of the organofunctional silane, is reacted with polyacrylate and/or polymethacrylate. Furthermore, at least 90% or at least 95% of the organofunctional silane is preferably present in a form reacted with polyacrylate and/or polymethacrylate. Furthermore, it is preferred if the reaction is carried out to 100%.

In further preferred embodiments, the polyacrylate and/or polymethacrylate is built up with or of compounds with several acrylate and/or methacrylate groups. In particular embodiments, it has proved to be advantageous in particular if the acrylate and/or methacrylate starting compounds used have two or more acrylate and/or methacrylate groups.

The above-named synthetic resin coatings according to the invention can contain further monomers and/or polymers in addition to the above-named acrylate and/or methacrylate compounds. The proportion of acrylate and/or methacrylate compounds including organofunctional silane is preferably at least 70 wt.-%, further preferably at least 80 wt.-%, still further preferably at least 90 wt.-%, in each case relative to the total weight of the synthetic resin coating. According to a preferred variant, the synthetic resin coating is built up exclusively of acrylate and/or methacrylate compounds and one or more organofunctional silanes, wherein additives such as corrosion inhibitors, colored pigments, dyes, UV stabilizers, etc. or mixtures thereof can also additionally be contained in the synthetic resin coating.

In particular embodiments, it is preferred that the synthetic resin layers according to the invention with several acrylate groups and/or methacrylate groups have in each case at least three acrylate and/or methacrylate groups. Furthermore, these starting compounds can preferably also have in each case four or five acrylate and/or methacrylate groups.

In particular embodiments, it is preferred in particular that polyfunctional acrylates and/or methacrylates are used for the production of the synthetic resin layer according to the invention. It has been shown that the synthetic resin layers according to the invention in which 2 to 4 acrylate and/or methacrylate groups are contained per acrylate and/or methacrylate starting compound surprisingly have an exceptional density and strength, without being brittle. 3 acrylate and/or methacrylate groups per acrylate and/or methacrylate starting compound have proved to be extremely suitable. Such optimized properties have proved to be particularly advantageous in order to provide a synthetic resin coating which is also suitable for conveying methods in which the particles is led through pipes for example in the form of an aerosol and in which multiple impacts of the individual particles on the pipe walls occur.

In particular embodiments, it is preferred in particular that the weight ratio of polyacrylate and/or polymethacrylate to organofunctional silane is 10:1 to 0.5:1.

Furthermore, the weight ratio of polyacrylate and/or polymethacrylate to organofunctional silane preferably lies in a range of from 7:1 to 1:1.

Examples of suitable difunctional acrylates are: allyl methacrylate, bisphenol A dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, diethylene glycol dimethacrylate, diurethane dimethacrylate, dipropylene glycol diacrylate, 1,12-dodecanediol dimethacrylate, ethylene glycol dimethacrylate, methacrylic acid anhydride, N,N-methylene-bis-methacrylamide neopentyl glycol dimethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol-200-diacrylate, polyethylene glycol-400-diacrylate, polyethylene glycol-400-dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, tricyclodecane dimethanol diacrylate, tripropylene glycol diacrylate, triethylene glycol dimethacrylate or mixtures thereof.

According to the invention, e.g. pentaerythritol triacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, tris-(2-hydroxyethyl)isocyanurate triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate or of mixtures thereof can be used as higher functional acrylates.

Trifunctional acrylates and/or methacrylates are particularly preferred.

According to the invention for example (methacryloxymethyl)methyldimethoxysilane, methacryloxymethyltrimethoxysilane, (methacryloxymethyl)methyldiethoxysilane, methacryloxymethyltriethoxysilane, 2-acryloxyethylmethyldimethoxysilane, 2-methacryloxyethyltrimethoxysilane, 3-acryloxypropylmethyldimethoxysilane, 2-acryloxyethyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltripropoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriacetoxysilane, 3-methacryloxypropymethyldimethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane vinyldimethoxymethylsilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, vinyltriacetoxysilane or mixtures thereof can be used as organofunctional silanes. Acrylate- and/or methacrylate-functional silanes are particularly preferred. In particular embodiments, 2-methacryloxyethyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, (methacryloxymethyl)methyldimethoxysilane, vinyltrimethoxysilane or mixtures thereof in particular have proved to be particularly suitable organofunctional silanes.

It has surprisingly been shown that, with the powdered coating materials according to the invention, even very thin layer thicknesses of the above-named synthetic resin layer are sufficient to guarantee a high chemical and mechanical stability of the particles according to the invention. At the same time, the use of such thin layers makes it possible, even at low temperatures and with only a short residence in the combustion flame or plasma flame, for such a coating to be removed or at least loosened to such an extent that the material used for the coating is not contained as an impurity in the coating or is present at least in such a small quantity that there is no noticeable impairment of the properties of the coating produced by means of the coating method. In particular embodiments, however, it is preferred in particular that the layer thickness and the composition of the synthetic resin layer are selected such that no detectable residues of the synthetic resin layer are contained in the coating produced in the coating method.

The further plastics named above by way of example are known to a person skilled in the art and can be selected on the basis of the invention disclosed herein in order to provide the effect according to the invention.

Examples of polycarbonates and the production thereof can be found in DE 1 300 266 B1 (interfacial polycondensation) or DE 14 95 730 A1 (reaction of biphenyl carbonate with bisphenols).

In the case of polyoxyalkylene homo- or copolymers, the polymer main chain has at least 50 mol.-% recurring units of —CH₂O—. A particular example of this plastic group is constituted by (co)polyoxymethylenes (POM). The homopolymers can be produced, preferably catalytically, for example by polymerization of formaldehyde or trioxane.

Examples of the above-named polyolefins are polyethylene and polypropylene as well as copolymers based on ethylene or propylene, optionally also with higher α-olefins. The term “polyolefin” within the meaning of the present invention also comprises in particular ethylene-propylene elastomers and ethylene-propylene terpolymers.

Examples of the above-named polyarylene ethers are polyarylene ethers per se, polyarylene ether sulfides, polyarylene ether sulfones and polyarylene ether ketones. The arylene groups here can be the same or different, and independently of each other can be for example an aromatic radical with 6 to 18 C atoms. Arylene radicals named by way of example are phenylene, bisphenylene, terphenylene, 1,5-naphthylene, 1,6-naphthylene, 1,5-anthrylene, 9,10-anthrylene or 2,6-anthrylene. Specific information in respect of the production of polyarylene ether sulfones is found for example in EP 113 112 A1 and EP 135 130 A2.

In particular embodiments, it is preferred in particular to use copolymers or block copolymers based on lactic acid and further monomers as polylactides.

The term “polyamides” within the meaning of the present invention comprises for example polyetheramides such as polyether block amides, polycaprolactams, polycapryllactams, polylaurolactams and polyamides which are obtained by reacting dicarboxylic acids with diamines. Disclosures in respect of the production of polyetheramides are found for example in U.S. Pat. No. 2,071,250, U.S. Pat. No. 2,071,251, U.S. Pat. No. 2,130,523, U.S. Pat. No. 2,130,948, U.S. Pat. No. 2,241,322, U.S. Pat. No. 2,312,966, U.S. Pat. No. 2,512,606 and U.S. Pat. No. 3,393,210. Dicarboxylic acids which can be reacted with the above-named diamines are for example alkanedicarboxylic acids with 6 to 12, in particular 6 to 10 carbon atoms and aromatic dicarboxylic acids. Suitable diamines are for example alkanediamines with 6 to 12, in particular 6 to 8 carbon atoms, as well as m-xylylenediamine, di-(4-aminophenyl)methane, di-(4-aminocyclohexyl)methane, 2,2-di-(4-aminophenyl)propane or 2,2-di-(4-aminocyclohexyl)propane.

Examples of vinylaromatic (co)polymers known to a person skilled in the art are polystyrene, styrene-acrytnitrile copolymers (SAN), impact-modified polystyrene (HIPS=High Impact Polystyrene) and ASA, ABS and AES polymers (ASA=acrylonitrile-styrene-acrylester, ABS=acrylonitrile-butadiene-styrene, AES=acrylonitrile-EPDM rubber-styrene). Examples of disclosures of the production of such plastics are found in EP-A-302 485, DE 197 28 629 A1, EP 99 532 A2, U.S. Pat. No. 3,055,859 and U.S. Pat. No. 4,224,419.

Examples of halogen-containing polymers are polymers of vinyl chloride, in particular polyvinyl chloride (PVC) such as hard PVC and soft PVC, and copolymers of vinyl chloride such as PVC-U molding compounds.

Polyester plastics which can be selected according to the invention are likewise known per se and described in the literature. The polyesters can be produced by reacting aromatic dicarboxylic acids, esters thereof or other ester-forming derivatives of same with aliphatic dihydroxy compounds in a manner known per se. In particular embodiments, naphthalene dicarboxylic acid, terephthalic acid and isophthalic acid or mixtures thereof are used as dicarboxylic acids. Up to 10 mol.-% of the aromatic dicarboxylic acids can be replaced by aliphatic or cycloaliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, dodecane diacids and cyclohexane dicarboxylic acids. Examples of aliphatic dihydroxy compounds are diols with 2 to 6 carbon atoms, in particular 1,2-ethanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-hexanediol, 1,4-cyclohexanediol and neopentyl glycol or mixtures thereof.

Examples of the polymers containing imide groups are polyimides, polyetherimides, and polyamide-imides. Such polymers are described for example in Römpp Chemie Lexikon, CD-ROM version 1.0, Thieme Verlag Stuttgart 1995.

Furthermore, for example fluorine-containing polymers such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoropropylene copolymers (FEP), copolymers of tetrafluoroethylene with perfluoroalkyl vinyl ether, ethylene-tetrafluoroethylene copolymers (ETFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polychlorotrifluoroethylene (PCTFE) and ethylene-chlorotrifluoroethylene copolymers (ECTFE) can be used.

The above-named thermoplastic elastomers (TPE) are characterized in that they can be processed like thermoplastics but have rubber-elastic properties. More detailed information is found for example in G. Holden et al., Thermoplastic Elastomers, 2^nd edition, Hanser Verlag, Munich 1996. Examples are thermoplastic polyurethane elastomers (TPE-U or TPU), styrene oligoblock copolymers (TPE-S) such as SBS (styrene-butadiene-styrene-oxy block copolymer) and SEES (styrene-ethylene-butylene-styrene block copolymer, obtainable by hydrogenation of SBS), thermoplastic polyolefin elastomers (TPE-O), thermoplastic polyester elastomers (TPE-E), thermoplastic polyamide elastomers (TPE-A) and thermoplastic vulcanizates (TPE-V).

In particular embodiments, it is preferred that the polymers used as coating additives have a molecular weight of at most 200,000, preferably of at most 170,000, more preferably of at most 150,000 and still more preferably at most 130,000. In particular ones of the above-named embodiments, it is preferred in particular that the compounds used as coating additives have a molecular weight of at most 110,000, preferably of at most 90,000, more preferably of at most 70,000 and still more preferably of at most 50,000.

The above-named carboxylic acids used as coating additive also comprise in particular dicarboxylic acids, tricarboxylic acids and tetracarboxylic acids in particular embodiments. Examples of dicarboxylic acids are succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid.

In particular preferred embodiments, the above-named carboxylic acid derivatives are directed in particular towards carboxylic acid esters.

Examples of the above-named fatty acids are capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, melissic acid, undecylenic acid, palmitoleic acid, elaidic acid, vaccenic acid, eicosenoic acid, cetoleic acid, erucic acid, nervonic acid, sorbic acid, linoleic acid, linolenic acid, eleostearic acid, arachidonic acid, timnodonic acid, clupanodonic acid, docosahexaenoic acid, stearic acid and oleic acid. In particular quite particularly preferred embodiments of the present invention, the coating additives comprise no stearic acid or oleic acid, preferably no saturated or unsaturated C18 carboxylic acids, more preferably no saturated or unsaturated C14 to C18 carboxylic acids, still more preferably no saturated or unsaturated C12 to C18 carboxylic acids and most preferably no saturated or unsaturated C10 to C20 carboxylic acids. The term “C” followed by a number relates within the meaning of the present invention to the carbon atoms contained in a molecule or molecule constituent, wherein the number expresses the quantity of carbon atoms.

The above-named phosphonic acids are expressed by Formula (I):

(X)_mP(=0)Y_nR_(3-m)  (I),

wherein m is 0, 1 or 2, n is 0 or 1, X can be the same or different and is hydrogen, hydroxy, halogen or —NR′₂, R′ can be the same or different and is hydrogen, a substituted or unsubstituted C1-C9 alkyl group or a substituted or unsubstituted aryl group, Y can be the same or different and is —O—, —S—, —NH— or —NR— and R can be the same or different and is selected from the group consisting of C1-C30 alkyl groups, C2-C30 alkenyl groups, C2-C30 alkinyl groups, C5-C30 aryl groups, C6-C30 arylalkyl groups, C4-C30 heteroaryl groups, C5-C30 heteroarylalkyl groups, C3-C30 cycloalkyl groups, C4-C30 cycloalkylalkyl groups, C2-C30 heterocycloalkyl groups, C3-C30 heterocycloalkylalkyl groups, C1-C30 ester groups, C1-C30 alkyl ether groups, C1-C30 cycloalkyl ether groups, C1-C30 cycloalkenyl ether groups, C6-C30 aryl ether groups, C7-C30 arylalkyl ether groups, wherein the above-named groups can be substituted or unsubstituted and optionally straight-chained or branched.

The term “substituted” within the meaning of the present invention describes that at least one hydrogen atom of the relevant group by a halogen, hydroxy, cyano, C1-C8 alkyl, C2-C8 alkenyl, C2-C8 alkinyl, C1-C5 alkanoyl, C3-C8 cycloalkyl, heterocyclic, aryl, heteroaryl, C1-C7 alkylcarbonyl, C1-C7 alkoxy, C2-C7 alkenyloxy, C2-C7 alkinyloxy, aryloxy, acyl, C1-C7 acryloxy, C1-C7 methacryloxy, C1-C7 epoxy, C1-C7 vinyl, C1-C5 alkoxycarbonyl, aroyl, aminocarbonyl, alkylaminocarbonyl, dialkylaminocarbonyl, amincarbonyloxy, C1-C7 alkylaminocarbonyloxy, C1-C7 dialkylamincarbonyloxy, C1-C7 alkanoylamine, C1-C7 alkoxycarbonylamine, C1-C7 alkylsulfonylamine, aminosulfonyl, C1-C7 alkylaminosulfonyl, C1-C7 dialkylaminsulfonyl, carboxy, cyano, trifluoromethyl, trifluoromethoxy, nitro, sulfonic acid, phosphoric acid, amine; amide; the nitrogen atom optionally, independently of each other, substituted once or twice with C1-C5 alkyl or aryl groups; ureido; the nitrogen atoms optionally, independently of each other, substituted once or twice with C1-C5 alkyl or aryl groups; or C1-C5 alkylthio group.

The terms “cycloalkyl group” and “heterocycloalkyl group” within the meaning of the present invention comprise saturated, partially saturated and unsaturated systems, apart from aromatic systems, which are called “aryl groups” or “heteroaryl groups”.

The term “alkyl” within the meaning of the present invention, unless otherwise indicated, preferably represents straight or branched C1 to C27, more preferably straight or branched C1 to C25 and still more preferably straight or branched C1 to C20 carbon chains. The terms “alkenyl” and “alkinyl” within the meaning of the present invention, unless otherwise indicated, preferably represent straight or branched C2 to C27, more preferably straight or branched C2 to C25 and still more preferably straight or branched C2 to C20 carbon chains. The term “aryl” within the meaning of the present invention represents aromatic carbon rings, preferably aromatic carbon rings with at most 7 carbon atoms, more preferably the phenyl ring, wherein the above-named aromatic carbon rings can be a constituent of a condensed ring system. Examples of aryl groups are phenyl, hydroxyphenyl, biphenyl and naphthyl. The term “heteroaryl” within the meaning of the present invention represents aromatic rings, in which a carbon atom of an analogous aryl ring has formally been replaced by a heteroatom, preferably by an atom selected from the group consisting of O, S and N.

The above-named silanes are characterized by a structure according to Formula (II):

R_pSiX_(4-p)  (II),

wherein p is 0, 1, 2 or 3, X can be the same or different and is hydrogen, hydroxy, halogen or —NR′₂, R′ can be the same or different and is hydrogen, a substituted or unsubstituted C1-C9 alkyl group or a substituted or unsubstituted aryl group and R can be the same or different and is selected from the group consisting of C1-C30 alkyl groups, C2-C30 alkenyl groups, C2-C30 alkinyl groups, C5-C30 aryl groups, C6-C30 arylalkyl groups, C4-C30 heteroaryl groups, C5-C30 heteroarylalkyl groups, C3-C30 cycloalkyl groups, C4-C30 cycloalkylalkyl groups, C2-C30 heterocycloalkyl groups, C3-C30 heterocycloalkylalkyl groups, C1-C30 ester groups, C1-C30 alkyl ether groups, C1-C30 cycloalkyl ether groups, C1-C30 cycloalkenyl ether groups, C6-C30 aryl ether groups, C7-C30 arylalkyl ether groups, wherein the above-named groups can be substituted or unsubstituted and optionally straight-chained or branched.

The coating additive can be bound for example chemically or physically to the surface of the particles of the powdered coating material. It is not necessary here that an unbroken surface coverage of the particles is carried out, even if this is preferred in particular embodiments of the present invention.

In particular embodiments, it is preferred that the coating additives are bound as weakly as possible to the surface of the particles of the powdered coating material.

For example, in particular ones of the above-named embodiments, it is preferred that the coating additives used according to the invention carry no functional group. The term “functional group” within the meaning of the present invention denotes molecular groups in molecules which decisively influence the substance properties and the reaction behavior of the molecules. Examples of such functional groups are: carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, silane groups, carbonyl groups, hydroxyl groups, amine groups, hydrazine groups, halogen groups and nitro groups.

In particular other embodiments, in contrast, it is preferred that the coating additives cannot be removed from the surface too easily, for example as a result of friction. In particular ones of the above-named embodiments, it is preferred in particular that the coating additives used according to the invention carry at least one functional group, preferably at least two functional groups, more preferably at least three functional groups.

Additionally, it was surprisingly found that the use of the powdered coating material according to the invention with a surface coverage according to the invention can also be used coating materials with an unexpectedly high melting point. Without being understood as limiting the invention, the inventors are of the view that the more uniform conveying of the particles with reduced tendency to agglomerate allows the individual particles to strike the substrate surface and the kinetic energy present to be able to be utilized fully to shape the particle. In the case of a non-uniform, thus localized, application of agglomerates, some of the kinetic energy is possibly used up by the breakup of the agglomerate and particles that strike later are cushioned by coating material already present at this site, but not yet solidified. If the powdered coating material is passed through a flame beforehand, the thermal energy is furthermore probably better transferred to the particles in the case of uniform fed-in particles without agglomerates.

For example, in particular embodiments powdered coating materials covered according to the invention with at least one coating additive can also be used to produce homogeneous layers if the melting point, measured in [K], of the coating material is up to 50%, preferably up to 60%, more preferably up to 65% and still more preferably up to 70% of the temperature, measured in [K], of the medium used in the coating method directed onto the substrate, for example the gas stream, the combustion flame and/or the plasma flame. In particular ones of the above-named embodiments furthermore powdered coating materials covered according to the invention with at least one coating additive can also be used to produce homogeneous layers if the melting point, measured in [K], of the coating material is up to 75%, preferably up to 80%, more preferably up to 85% and still more preferably up to 90% of the temperature, measured in [K], of the medium used in the coating method directed onto the substrate, for example the gas stream, the combustion flame and/or the plasma flame. The above-named percentages relate to the ratio of the melting temperature of the coating material to the temperature of the gas stream in cold gas spraying, the combustion flame in flame spraying and high-speed flame spraying or the plasma flame in non-thermal or thermal plasma spraying in [K]. The thus-obtained coating has only a few free particle or grain structures, preferably none. The above-named homogeneous layers are characterized in that the produced layers have less than 10%, preferably less than 5%, more preferably less than 3%, still more preferably less than 1% and most preferably less than 0.1% cavities. In particular, it is preferred that no cavities at all are recognizable. The above-named term “cavity” within the meaning of the present invention describes the proportion of holes, incorporated in the coating, on the two-dimensional surface of a cross-section of the coated substrate, relative to the coating contained in the two-dimensional surface. A determination of this proportion is carried out by means of SEM at 30 randomly selected sites on the coating, wherein for example a length of 100 μm of the substrate coating is examined.

It was surprisingly found that, through the use of the powdered coating material according to the invention, homogeneous coatings could also be produced from materials which have a strong tendency to form agglomerates for example because of their particle-size distributions and which tend to form non-homogeneous coatings as a result of a lack of breakup of the above-named agglomerates.

The size distribution of the particles is preferably determined by means of laser granulometry. In this method, the particles can be measured in the form of a powder. The scattering of the irradiated laser light is detected in different spatial directions and evaluated according to the Fraunhofer diffraction theory. The particles are treated computationally as spheres. Thus, the determined diameters always relate to the equivalent spherical diameter determined over all spatial directions, irrespective of the actual shape of the particles. The size distribution is determined, calculated in the form of a volume average relative to the equivalent spherical diameter. This volume-averaged size distribution can be represented as a cumulative frequency distribution. The cumulative frequency distribution is characterized in a simplified manner by different characteristic values, for example the D₁₀, D₅₀ or D₉₀ value.

The measurements can be carried out for example with the particle-size analyzer HELOS from Sympatec GmbH, Clausthal-Zellerfeld, Germany. Here, a dry powder can be dispersed using a dispersing unit of the Rodos T4.1 type at a primary pressure of for example 4 bar. Alternatively, a size distribution curve of the particles can be measured, for example, with a device from Quantachrome (device: Cilas 1064) according to the manufacturers instructions. For this, 1.5 g of the powdered coating material is suspended in approx. 100 ml isopropanol, treated for 300 seconds in an ultrasound bath (device: Sonorex IK 52, Bandelin) and then introduced by means of a Pasteur pipette into the sample preparation cell of the measuring device and measured several times. The resultant average values are formed from the individual measurement results. The scattered light signals are evaluated according to the Fraunhofer method.

In particular embodiments of the invention, it is preferred that the powdered coating material has a particle-size distribution with a D₅₀ value of at most 53 μm, preferably at most 51 μm, more preferably at most 50 μm and still more preferably at most 49 μm. In particular ones of the above-named embodiments, it is preferred in particular that the powdered coating material has a particle-size distribution with a D₅₀ value of at most 48 μm, preferably at most 47 μm, more preferably at most 46 μm and still more preferably at most 45 μm.

The term “D₅₀” within the meaning of the present invention denotes the particle size at which 50% of the above-named particle-size distribution volume-averaged by means of laser granulometry lies below the indicated value. The measurements can be carried out for example according to the above-named measurement method with a particle-size analyzer HELOS from Sympatec GmbH, Clausthal-Zellerfeld, Germany.

In particular embodiments of the invention, it is preferred in particular that the powdered coating material has a particle-size distribution with a D₅₀ value of at least 1.5 μm, preferably at least 2 μm, more preferably at least 4 μm and still more preferably at least 6 μm. In particular ones of the above-named embodiments, it is preferred in particular that the powdered coating material has a particle-size distribution with a D₅₀ value of at least 7 μm, preferably at least 9 μm, more preferably at least 11 μm and still more preferably at least 13 μm.

In particular embodiments, it is furthermore preferred that the powder has a particle-size distribution with a D₅₀ value from a range of from 1.5 to 53 μm, preferably from a range of from 2 to 51 μm, more preferably from a range of from 4 to 50 μm and still more preferably from a range of from 6 to 49 μm. In particular ones of the above-named embodiments, it is preferred in particular that the powder has a particle-size distribution with a D₅₀ value from a range of from 7 to 48 μm, preferably from a range of from 9 to 47 μm, more preferably from a range of from 11 to 46 μm and still more preferably from a range of from 13 to 45 μm.

In other embodiments, it is preferred for example that the powder has a particle-size distribution with a D₅₀ value from a range of from 1.5 to 45 μm, preferably from a range of from 2 to 43 μm, more preferably from a range of from 2.5 to 41 μm and still more preferably from a range of from 3 to 40 μm. In particular ones of the above-named embodiments, it is preferred in particular that the powder has a particle-size distribution with a D₅₀ value from a range of from 3.5 to 38 μm, preferably from a range of from 4 to 36 μm, more preferably from a range of from 4.5 to 34 μm and still more preferably from a range of from 5 to 32 μm.

In still other embodiments, in contrast, it is preferred for example that the powder has a particle-size distribution with a D₅₀ value from a range of from 9 to 53 μm, preferably from a range of from 12 to 51 μm, more preferably from a range of from 15 to 50 μm, still more preferably from a range of from 17 to 49 μm. In particular ones of the above-named embodiments, it is preferred in particular that the powder has a particle-size distribution with a D₅₀ value from a range of from 19 to 48 μm, preferably from a range of from 21 to 47 μm, more preferably from a range of from 23 to 46 μm and still more preferably from a range of from 25 to 45 μm.

In further particular embodiments of the invention, it is preferred that the powdered coating material has a particle-size distribution with a D₉₀ value of at most 103 μm, preferably at most 99 μm, more preferably at most 95 μm, still more preferably at most 91 μm and most preferably at most 87 μm. In particular ones of the above-named embodiments, it is preferred in particular that the powdered coating material has a D₉₀ value of at most 83 μm, preferably at most 79 μm, more preferably at most 75 μm and still more preferably at most 71 μm.

The term “D₉₀” within the meaning of the present invention denotes the particle size at which 90% of the above-named particle-size distribution volume-averaged by means of laser granulometry lies below the indicated value. The measurements can be carried out for example according to the above-named measurement method with a particle-size analyzer HELOS from Sympatec GmbH, Clausthal-Zellerfeld, Germany.

In particular embodiments, it is therefore preferred that the powdered coating material has a particle-size distribution with a D₉₀ value of at least 9 μm, preferably at least 11 μm, more preferably at least 13 μm and still more preferably at least 15 μm. In particular ones of the above-named embodiments, it is preferred in particular that the powdered coating material has a particle-size distribution with a D₉₀ value of at least 17 μm, preferably at least 19 μm, more preferably at least 21 μm and still more preferably at least 22 μm.

According to particular preferred embodiments, the powdered coating materials have a particle-size distribution with a D₉₀ value from a range of from 42 to 103 μm, preferably from a range of from 45 to 99 μm, more preferably from a range of from 48 to 95 μm and still more preferably from a range of from 50 to 91 μm. In particular ones of the above-named embodiments, it is preferred in particular that the powdered coating material has a D₉₀ value from a range of from 52 to 87 μm, preferably from a range of from 54 to 81 μm, more preferably from a range of from 56 to 75 μm and still more preferably from a range of from 57 to 71 μm.

In further particular embodiments, it is preferred that the powdered coating material has a particle-size distribution with a D₁₀ value of at most 5 μm, preferably at most 4 μm, more preferably at most 3 μm and still more preferably at most 2.5 μm. In particular ones of the above-named embodiments, it is preferred in particular that the powdered coating material has a particle-size distribution with a D₁₀ value of at most 2.2 μm, preferably at most 2 μm, more preferably at most 1.8 μm and still more preferably at most 1.7 μm.

The term “D₁₀” within the meaning of the present invention denotes the particle size at which 10% of the above-named particle-size distribution volume-averaged by means of laser granulometry lies below the indicated value. The measurements can be carried out for example according to the above-named measurement method with a particle-size analyzer HELOS from Sympatec GmbH, Clausthal-Zellerfeld, Germany.

On the other hand, the powdered coating materials according to the invention with a high fines proportion also still have a strong tendency to form fine dusts, which makes the handling of corresponding powders much more difficult. In particular embodiments, therefore, it is preferred that the powdered coating material according to the invention has a particle-size distribution with a D₁₀ value of at least 0.2 μm, preferably at least 0.4 μm, more preferably at least 0.5 μm and still more preferably at least 0.6 μm. In particular ones of the above-named embodiments, it is preferred in particular that the powdered coating material according to the invention has a particle-size distribution with a D₁₀ value of at least 0.7 μm, preferably 0.8 μm, more preferably 0.9 μm and still more preferably at least 1.0 μm.

In particular preferred embodiments, the powdered coating material according to the invention is characterized in that it have a particle-size distribution with a D₁₀ value from a range of from at least 0.2 to 5 μm, preferably at least 0.4 to 4 μm, more preferably from a range of from 0.5 to 3 μm and still more preferably from a range of from 0.6 to 2.5 μm. In particular ones of the above-named embodiments, it is preferred in particular that the powdered coating material according to the invention has a particle-size distribution with a D₁₀ value from a range of from 0.7 to 2.2 μm, preferably from a range of from 0.8 to 2.1 μm, more preferably from a range of from 0.9 to 2.0 μm and still more preferably from a range of from 1.0 to 1.9 μm.

For example, in particular embodiments, it is preferred in particular that the powdered coating material has a particle-size distribution with a D₁₀ value of from 3.7 to 26 μm, a D₅₀ value of from 6 to 49 μm and a D₉₀ value of from 12 to 86 μm. In particular ones of the above-named embodiments, it is particularly preferred that the powdered coating material has a particle-size distribution with a D₁₀ value of from 5.8 to 26 μm, a D₅₀ value of from 11 to 46 μm and a D₉₀ value of from 16 to 83 μm. In particular ones of the above-named embodiments, it is still more preferred that the powdered coating material has a particle-size distribution with a D₁₀ value of from 9 to 19 μm, a D₅₀ value of from 16 to 35 μm and a D₉₀ value of from 23 to 72 μm.

In further particular embodiments, it is preferred for example that the powdered coating material has a particle-size distribution with a D₁₀ value of from 0.8 to 28 μm, a D₅₀ value of from 1.5 to 45 μm and a D₉₀ value of from 2.5 to 81 μm. In particular ones of the above-named embodiments, it is particularly preferred that the powdered coating material has a particle-size distribution with a D₁₀ value of from 2.2 to 22 μm, a D₅₀ value of from 4 to 36 μm and a D₉₀ value of from 4 to 62 μm. In particular ones of the above-named embodiments, it is still more preferred that the powdered coating material has a particle-size distribution with a D₁₀ value of from 2.8 to 17 μm, a D₅₀ value of from 6 to 28 μm and a D₉₀ value of from 9 to 49 μm.

In further particular embodiments, it is preferred for example that the powdered coating material has a particle-size distribution with a D₁₀ value of from 4.8 to 29 μm, a D₅₀ value of from 9 to 53 μm and a D₉₀ value of from 13 to 97 μm. In particular ones of the above-named embodiments, it is particularly preferred that the powdered coating material has a particle-size distribution with a D₁₀ value of from 12 to 26 μm, a D₅₀ value of from 23 to 46 μm and a D₉₀ value of from 35 to 87 μm. In particular ones of the above-named embodiments, it is still more preferred that the powdered coating material has a particle-size distribution with a D₁₀ value of from 15 to 24 μm, a D₅₀ value of from 28 to 44 μm and a D₉₀ value of from 41 to 78 μm.

Furthermore, it was observed that the conveyability of the powdered coating material according to the invention is dependent on the width of the particle-size distribution. This width can be calculated by indicating the so-called span value, which is defined as follows:

$\mathrm{Span}=\frac{D_{90}-D_{10}}{D_{50}}$

The inventors have found that in particular embodiments, for example, a still more uniform conveyability of the powdered coating material is achieved through the use of a powdered coating material with a smaller span, which further simplifies the formation of a more homogeneous and higher-quality layer. In particular embodiments, therefore, it is preferred that the span of the powdered coating material is at most 2.9, preferably at most 2.6, more preferably at most 2.4 and still more preferably at most 2.1. In particular ones of the above-named embodiments, it is preferred in particular that the span of the powdered coating material is at most 1.9, preferably at most 1.8, more preferably at most 1.7 and still more preferably at most 1.6.

On the other hand, the inventors have found that a very narrow span is not necessarily required to provide the sought conveyability, which makes the production of the powdered coating material easier. In particular embodiments, therefore, it is preferred that the span value of the powdered coating material is at least 0.4, preferably at least 0.5, more preferably at least 0.6 and still more preferably at least 0.7. In particular embodiments, it is preferred in particular that the span value of the powdered coating material is at least 0.8, preferably at least 0.9, more preferably at least 1.0 and still more preferably at least 1.1.

On the basis of the teaching disclosed herein, a person skilled in the art can select any combination, in particular of the above-named limit values of the span value, in order to provide the desired combination of properties. In particular embodiments, it is preferred for example that the powdered coating material has a span value from a range of from 0.4 to 2.9, preferably from a range of from 0.5 to 2.6, more preferably from a range of from 0.6 to 2.4 and still more preferably from a range of from 0.7 to 2.1. In particular ones of the above-named embodiments, it is preferred in particular that the powdered coating material has a span value from a range of from 0.8 to 1.9, preferably from a range of from 0.9 to 1.8, more preferably from a range of from 1.0 to 1.7 and still more preferably from a range of from 1.1 to 1.6.

A person skilled in the art is aware that, on the basis of the teaching disclosed herein, particular combinations of the span limit values or value ranges with the above-named preferred D₅₀ value ranges are preferred depending on the desired combination of advantages. In particular preferred embodiments, the powdered coating material has for example a particle-size distribution with a span from a range of from 0.4 to 2.9 and a D₅₀ value from a range of from 1.5 to 53 μm, preferably from a range of from 2 to 51 μm, more preferably from a range of from 4 to 50 μm, still more preferably from a range of from 6 to 49 μm and most preferably from a range of from 7 to 48 μm. In particular preferred ones of the above-named embodiments, the powdered coating material has a particle-size distribution with a span from a range of from 0.5 to 2.6 and a D₅₀ value from a range of from 1.5 to 53 μm, preferably from a range of from 2 to 51 μm, more preferably from a range of from 4 to 50 μm, still more preferably from a range of from 6 to 49 μm and most preferably from a range of from 7 to 48 μm. In particular further preferred embodiments, the powdered coating material has a particle-size distribution with a span from a range of from 0.6 to 2.4 and a D₅₀ value from a range of from 1.5 to 53 μm, preferably from a range of from 2 to 51 μm, more preferably from a range of from 4 to 50 μm, still more preferably from a range of from 6 to 49 μm and most preferably from a range of from 7 to 48 μm. In particular still further preferred embodiments, the powdered coating material has a particle-size distribution with a span from a range of from 0.7 to 2.1 and a D₅₀ value from a range of from 1.5 to 53 μm, preferably from a range of from 2 to 51 μm, more preferably from a range of from 4 to 50 μm, still more preferably from a range of from 6 to 49 μm and most preferably from a range of from 7 to 48 μm.

Furthermore, it was found that the density of the powdered coating material can influence the conveying of such powders in the form of an aerosol. Without being understood as limiting the invention, the inventors are of the view that the differences in inertia of particles that are the same size but have different densities lead to a different behavior of the aerosol streams of powdered coating materials with identical particle-size distribution. It can therefore prove to be difficult to transfer conveying methods which have been optimized for a specific D₅₀ to powdered coating materials with other densities. In particular embodiments, therefore, it is preferred that the upper limit of the span value is corrected dependent on the density of the powdered coating material used.

${\mathrm{Span}}_{\mathrm{UC}}={\mathrm{Span}}_U·{\left(\frac{{\rho }_{\mathrm{Alu}}}{{\rho }_X}\right)}^{\frac{1}{3}}$

Here, Span_UC is the corrected upper span value, Span_U is the upper span value, ρ_Alu is the density of aluminum (2.7 g/cm³) and ρ_X is the density of the powdered coating material used. However, it was furthermore found that the differences in the case of powdered coating materials with a lower density than aluminum are only slight, and a selection, optimized in this respect, of the powdered coating material does not result in a noticeable improvement in the conveyability. A powdered coating material with an uncorrected upper span value is therefore used for powdered coating materials with a density lower than the density of aluminum.

Coating methods that can be used according to the invention are known to a person skilled in the art under the names cold gas spraying, thermal plasma spraying, non-thermal plasma spraying, flame spraying and high-speed flame spraying.

Cold gas spraying is characterized in that the powder to be applied is not melted in the gas jet, but the particles are greatly accelerated and, as a result of their kinetic energy, form a coating on the surface of the substrate. Here, various gases known to a person skilled in the art can be used as carrier gas, such as nitrogen, helium, argon, air, krypton, neon, xenon, carbon dioxide, oxygen or mixtures thereof. In particular variants, it is preferred in particular that air, helium or mixtures thereof are used as gas.

Gas speeds of up to 3000 m/s are achieved through a controlled expansion of the above-named gases in a corresponding nozzle. The particles can be accelerated here to up to 2000 m/s. However, in particular variants of cold gas spraying, it is preferred that the particles achieve speeds for example of between 300 m/s and 1600 m/s, preferably between 1000 m/s and 1600 m/s, more preferably between 1250 m/s and 1600 m/s.

A disadvantage is, for example, the strong generation of noise which is brought about by the high speeds of the gas streams used.

In flame spraying, for example, a powder is converted to the liquid or plastic state by means of a flame and then applied to a substrate as coating. Here, e.g. a mixture of oxygen and a combustible gas such as acetylene or hydrogen is combusted. In particular variants of flame spraying, some of the oxygen is used to transport the powdered coating material into the combustion flame. The particles achieve speeds of between 24 and 31 m/s in customary variants of this method.

Similarly to flame spraying, in high-speed flame spraying, for example, a powder is also converted to the liquid or plastic state by means of a flame. However, the particles are accelerated to significantly higher speeds compared with the above-named method. In specific examples of the above-named method, for example, a speed of the gas stream of from 1220 to 1525 m/s with a speed of the particles of from approx. 550 to 795 m/s is named. In further variants of this method, however, gas speeds of over 2000 m/s are also achieved. In general, in customary variants of the previous method, it is preferred that the speed of the flame lies between 1000 and 2500 m/s. Furthermore, in customary variants, it is preferred that the flame temperature lies between 2200° C. and 3000° C. The temperature of the flame is thus comparable to the temperature in flame spraying. This is achieved by combusting the gases under a pressure of from approx. 515 to 621 kPa, followed by expansion of the combustion gases in a nozzle. In general, the view is taken that coatings produced here have a higher density than, for example, coatings obtained by the flame spraying method.

Detonation/explosive flame spraying can be viewed as a subtype of high-speed flame spraying. Here, the powdered coating material is strongly accelerated by repeated detonations of a gas mixture such as acetylene/oxygen, wherein for example particle speeds of approx. 730 m/s are achieved. The detonation frequency of the method here becomes for example between approx. 4 and 10 Hz. In variants such as the so-called high frequency gas detonation spraying, however, detonation frequencies of around approx. 100 Hz are also chosen.

The layers obtained are usually supposed to have a particularly high hardness, strength, density and good binding to the substrate surface. A disadvantage in the above-named methods is the increased safety costs, as well as for example the high noise load because of the high gas speeds.

In thermal plasma spraying, for example, a direct current arc furnace is passed through by a primary gas such as argon at a speed of 40 l/min and a secondary gas such as hydrogen at a speed of 2.5 l/min, wherein a thermal plasma is generated. Then, for example, 40 g/min of the powdered coating material is fed in with the aid of a carrier gas stream, which is passed into the plasma flame at a speed of 4 l/min. In usual variants of thermal plasma spraying, the conveying rate of the powdered coating material is between 5 g/min and 60 g/min, more preferably between 10 g/min and 40 g/min.

In particular variants of the method, it is preferred to use argon, helium or mixtures thereof as ionizable gas. The whole gas stream is furthermore preferably 30 to 150 SLPM (standard liters per minute) in particular variants. The electrical power used to ionize the gas stream, without the heat energy dissipated as a result of cooling, can be selected for example between 5 and 100 kW, preferably between 40 and 80 kW. Here, plasma temperatures of between 4000 and a few 10000 K can be achieved.

In non-thermal plasma spraying, a non-thermal plasma is used to activate the powdered coating material. The plasma used here is generated for example with a barrier discharge or corona discharge with a frequency of from 50 Hz to 1 MHz. In particular variants of non-thermal plasma spraying, it is preferred that work is done at a frequency of from 10 kHz to 100 kHz. The temperature of the plasma here is preferably less than 3000 K, preferably less than 2500 K and still more preferably less than 2000 K. This minimizes the technical outlay and keeps the input of energy into the coating material to be applied as low as possible, which in turn allows a gentle coating of the substrate. The order of magnitude of the temperature of the plasma flame is thus preferably comparable to that of flame spraying or of high-speed flame spraying. Non-thermal plasmas the core temperature of which is below 1173 K or even below 773 K in the core region can also be generated by targeted choice of the parameters. The temperature in the core region is measured here, for example, using an NiCr/Ni thermocouple and a spray diameter of 3 mm at a distance of 10 mm from the nozzle outlet in the core of the emerging plasma jet at ambient pressure. Such non-thermal plasmas are suitable in particular for coatings of very temperature-sensitive substrates.

To produce coatings with sharp boundaries without the need to cover areas in a targeted manner, it has proved to be advantageous to design, in particular, the outlet opening for the plasma flame such that the track widths of the coatings produced lie between 0.2 mm and 10 mm. This makes a very precise, flexible, energy-efficient coating possible while making the best possible use of the coating material used. For example, a distance of 1 mm is chosen as the distance from the spray lance to the substrate. This makes possible as great a flexibility as possible of the coatings and, at the same time, guarantees high-quality coatings. The distance between spray lance and substrate expediently lies between 1 mm and 35 mm.

Various gases known to a person skilled in the art and mixtures thereof can be used as ionizable gas in the non-thermal plasma method. Examples of these are helium, argon, xenon, nitrogen, oxygen, hydrogen or air, preferably argon or air. A particularly preferred ionizable gas is air.

For example to reduce the noise load, it can also be preferred here that the speed of the plasma stream lies below 200 m/s. For example, a value of between 0.01 m/s and 100 m/s, preferably between 0.2 m/s and 10 m/s, can be chosen as the flow rate. In particular embodiments, it is preferred in particular for example that the volume flow of the carrier gas lies between 10 and 25 l/min, more preferably between 15 and 19 l/min.

According to a preferred embodiment, the particles of the powdered coating material are preferably metallic particles or metal-containing particles. It is preferred in particular that the metal content of the metallic particles or metal-containing particles is at least 95 wt.-%, preferably at least 99 wt.-%, still more preferably at least 99.9 wt.-%. In particular preferred embodiments, the metal is, or the metals are, selected from the group consisting of silver, gold, platinum, palladium, vanadium, chromium, manganese, cobalt, germanium, antimony, aluminum, zinc, tin, iron, copper, nickel, titanium, silicon, alloys and mixtures thereof. In particular ones of the above-named embodiments, it is preferred in particular that the metal is, or the metals are, selected from the group consisting of silver, gold, aluminum, zinc, tin, iron, copper, nickel, titanium, silicon, alloys and mixtures thereof, preferably from the group consisting of silver, gold, aluminum, zinc, tin, iron, nickel, titanium, silicon, alloys and mixtures thereof.

According to further preferred embodiments of the method according to the invention, the metal or the metals of the particles of the powdered coating material is or are selected from the group consisting of silver, aluminum, zinc, tin, copper, alloys and mixtures thereof. In particular, metallic particles or metal-containing particles in which the metal is, or the metals are, selected from the group consisting of silver, aluminum and tin have proved to be particularly suitable particles in specific embodiments.

In further embodiments of the invention, the powdered coating material consists of inorganic particles which are preferably selected from the group consisting of carbonates, oxides, hydroxides, carbides, halides, nitrides and mixtures thereof. Mineral and/or metal-oxide particles are particularly suitable.

In other embodiments, the inorganic particles are alternatively or additionally selected from the group consisting of carbonaceous particles or graphite particles.

A further possibility is the use of mixtures of the metallic particles and the above-named inorganic particles, such as for example mineral and/or metal-oxide particles, and/or the particles which are selected from the group consisting of carbonates, oxides, hydroxides, carbides, halides, nitrides and mixtures thereof.

Furthermore, the powdered coating material can comprise or consist of glass particles. In particular embodiments, it is preferred in particular that the powdered coating material comprises or consists of coated glass particles.

In addition, in particular embodiments, the powdered coating material comprises or consists of organic and/or inorganic salts.

In still other embodiments of the present invention, the powdered coating material comprises or consists of plastic particles. The above-named plastic particles are formed for example from pure or mixed homo-, co-, block or pre-polymers or mixtures thereof. Here, the plastic particles can be pure crystals or be mixed crystals or have amorphous phases. The plastic particles can be obtained for example by mechanical comminution of plastics.

In particular embodiments of the method according to the invention, the powdered coating material comprises or consists of mixtures of particles of different materials. In particular preferred embodiments, the powdered coating material consists in particular of at least two, preferably three, different particles of different materials.

The particles can be produced via different methods. For example, the metal particles can be obtained by nebulizing or atomizing molten metals. Glass particles can be produced by mechanical comminution of glass or else from the melt. In the latter case, the glass melt can likewise be atomized or nebulized. Alternatively, melted glass can also be comminuted on rotating elements, for example a drum.

Mineral particles, metal-oxide particles and inorganic particles which are selected from the group which consists of oxides, hydroxides, carbonates, carbides, nitrides, halides and mixtures thereof can be obtained by comminuting the naturally occurring minerals, stones, etc. and then screening them by size.

The screening by size can be carried out for example by means of cyclones, air separators, screens, etc.

In particular embodiments of the present invention, the particles of the powdered coating material have been equipped with a coating in addition to the surface coverage according to the invention. This makes it possible for example to provide a coated standard powder with an increased oxidation stability which is adapted to specific devices or uses by a targeted, subsequent surface coverage. This is particularly advantageous for a surface coverage according to the invention which is applied by means of methods that are simple in terms of process engineering. In particular embodiments, therefore, it is preferred in particular that the above-named coating is applied before the surface coverage according to the invention, wherein the surface coverage according to the invention is preferably applied mechanically to the particles, for example kneaded on.

In particular preferred embodiments of the present invention, the above-named coating can comprise a metal or consist of a metal. Such a coating of a particle can be formed closed or particulate, wherein coatings with a closed structure are preferred. The layer thickness of such a metallic coating preferably lies below 1 μm, more preferably below 0.8 μm and still more preferably below 0.5 μm. In particular embodiments, such coatings have a thickness of at least 0.05 μm, more preferably of at least 0.1 μm. Metals that are particularly preferred in particular embodiments for use in one of the above-named coatings, preferably as main constituents, are selected from the group consisting of copper, titanium, gold, silver, tin, zinc, iron, silicon, nickel and aluminum, preferably from the group consisting of gold, silver, tin and zinc, further preferably from the group consisting of silver, tin and zinc. The term main constituent within the meaning of the above-named coating denotes that the relevant metal or a mixture of the above-named metals represents at least 90 wt.-%, preferably 95 wt.-%, further preferably 99 wt.-% of the metal content of the coating. It must be understood that, in the case of a partial oxidation, the oxygen proportion of the corresponding oxide layer is not taken into account. Such metallic coatings can be produced for example by means of gas-phase synthesis or wet-chemical methods.

In further particular embodiments, the particles according to the invention of the powdered coating material are additionally or alternatively coated with a metal oxide layer. Preferably, this metal oxide layer substantially consists of silicon oxide, aluminum oxide, boron oxide, zirconium oxide, cerium oxide, iron oxide, titanium oxide, chromium oxide, tin oxide, molybdenum oxide, oxide hydrates thereof, hydroxides thereof and mixtures thereof. In particular preferred embodiments, the metal oxide layer substantially consists of silicon oxide. The above-mentioned term, “substantially consists of”, within the meaning of the present invention means that at least 90%, preferably at least 95%, more preferably at least 98%, still more preferably at least 99% and most preferably at least 99.9% of the metal oxide layer consists of the above-named metal oxides, in each case relative to the number of particles of the metal oxide layer, wherein any water contained is not factored in. The composition of the metal oxide layer can be determined by means of methods known to a person skilled in the art, such as for example sputtering in combination with XPS or TOF-SIMS. In particular ones of the above-named embodiments, it is preferred in particular that the metal oxide layer does not represent an oxidation product of a metal core located underneath it. Such a metal oxide layer can be applied for example using the sol-gel method.

In particular preferred embodiments, the substrate is selected from the group consisting of plastic substrates, inorganic substrates, cellulose-containing substrates and mixtures thereof.

The plastic substrates can be for example plastic films or shaped bodies made of plastics. The shaped bodies can have geometrically simple or complex shapes. The plastic shaped body can be for example a component from the automotive industry or the construction industry.

The cellulose-containing substrates can be cardboard, paper, wood, wood-containing substrates, etc.

The inorganic substrates can be for example metallic substrates, such as sheet metals or metallic shaped bodies or ceramic or mineral substrates or shaped bodies. The inorganic substrates can also be solar cells or silicon wavers, to which for example electrically conductive coatings or contacts are applied.

Substrates made of glass, such as for example glass panes, can also be used as inorganic substrates. The glass, in particular glass panes, can be equipped for example with electrochromic coatings using the method according to the invention.

The substrates coated by means of the method according to the invention are suitable for very different uses.

In particular embodiments, the coatings have optical and/or electromagnetic effects. Here, the coatings can bring about reflections or absorptions. Furthermore, the coatings can be electrically conductive, semiconductive or non-conductive.

Electrically conductive layers can be applied for example in the form of strip conductors to components. This can be used for example to make current-carrying possible within the framework of the on-board power supply in an automobile component. Furthermore, such a strip conductor can, however, also be formed for example as an antenna, as a shield, as an electrical contact, etc. This is particularly advantageous for example for RFID applications (radio frequency identification). Furthermore, coatings according to the invention can be used for example for heating purposes or for the targeted heating of specific components or specific parts of larger components.

In further particular embodiments, the coatings produced act as sliding layers, diffusion barriers for gases and liquids, wear and/or corrosion protection layers. Furthermore, the coatings produced can influence the surface tension of liquids or have adhesion-promoting properties.

The coatings produced according to the invention can furthermore be used as sensor surfaces, for example as human-machine interface (HMI), for example in the form of a touchscreen. The coatings can likewise be used to shield from electromagnetic interferences (EMI) or to protect against electrostatic discharges (ESD). The coatings can also be used to bring about electromagnetic compatibility (EMC).

Furthermore, through the use of the particles according to the invention, layers can be applied which are applied for example to increase the stability of corresponding components after repair. An example is constituted by repairs in the aviation sector, wherein for example a loss of material as a result of processing steps must be compensated for, or a coating is to be applied for example for stabilization. This proves to be difficult for aluminum components for example, and normally requires post-processing steps such as sintering. In contrast, by means of the methods according to the invention, firmly adhering coatings can be applied under very gentle conditions, without post-processing steps such as sintering even being required.

In still other embodiments, the coatings act as electrical contacts and allow an electrical connection between different materials.

A person skilled in the art is aware that the specifications indicated above with regard to the method according to the invention in respect of the powdered coating material and the particles contained therein also apply correspondingly to the use of the powdered coating material and the particles contained therein, and vice versa.

FIGURES

FIGS. 1 and 2 show a copper layer applied to a steel sheet.

EXAMPLES

Materials and methods used.

The size distribution of the particles of the powdered coating materials used was determined by means of a HELOS device (Sympatec, Germany). For the measurement, 3 g of the powdered coating material was introduced into the measuring device and treated, before the measurement, with ultrasound for 30 seconds. For the dispersion, a Rodos T4.1 dispersing unit was used, wherein the primary pressure was 4 bar. The evaluation was carried out with the device's standard software.

The method according to the invention is now explained in more detail with reference to the following examples, without being limited to the examples.

Example 1

Powdered Coating Materials Covered with 1,10-decanedicarboxylic acid

3 g of 1,10-decanedicarboxylic acid was used as coating additive and dissolved in 50 g ethyl acetate. This mixture was then introduced, together with 240 g aluminum particles (D₅₀=2 μm), into a kneader (Duplex kneader from IKA) and kneaded for 30 min at RT (20° C.). A temperature of 40° C. and a vacuum of 250 mbar were then set. Drying was carried out for 1 h and then the particles covered with the coating additive were removed from the kneader and then screened (71 μm).

Example 2

Powdered Coating Materials Covered with Monoethyl Fumarate

The application of the coating additive was carried out analogously to Example 1. 3 g monoethyl fumarate was used as coating additive.

Example 3

Powdered Coating Materials Covered with Adipic Acid Monoethyl Ester

The application of the coating additive was carried out analogously to Example 1. 3 g adipic acid monoethyl ester was used as coating additive.

Example 4

Powdered Coating Materials Covered with Methyl Triglycol

The application of the coating additive was carried out analogously to Example 1. 3 g methyl triglycol was used as coating additive.

Example 5

Powdered Coating Materials Covered with Adipic Acid Monoethyl Ester

The application of the coating additive was carried out analogously to Example 1. However, copper particles with a D₅₀ of 34 μm were used here. 3 g adipic acid monoethyl ester was used as coating additive.

Example 6

Powdered Coating Materials Covered with Methyl Triglycol

The application of the coating additive was carried out analogously to Example 1. However, a copper particle with a D₅₀ of 34 μm was used here. 3 g methyl triglycol was used as coating additive.

Example 7

Powdered Coating Materials Covered with Ethocel

7-1: Copper Particles

The application of the coating additive was carried out analogously to Example 1. Copper particles with a D₅₀ value of 34 μm were used here. 3 g ethyl cellulose (Ethocel Standard 10, from Dow Wolff Cellulosics) was used as coating additive.

7-2: Aluminum Particles

The application of the coating additive was carried out analogously to Example 1. 100 g aluminum particles with a D₅₀ value of 1.6 μm were used here. 3 g ethyl cellulose (Ethocel Standard 10, from Dow Wolff Cellulosics) was used as coating additive.

Example 8

Powdered Coating Materials Covered with Monoethyl Fumarate

The application of the coating additive was carried out analogously to Example 1. A copper particle with a D₅₀ value of 34 μm was used here. 3 g DEGALAN PM 381 (copolymer from methyl methacrylate and isobutyl methacrylate, from Evonik) was used as coating additive.

Example 9

Powdered Coating Materials Covered with Polyacrylate

The copper paste or tin paste was dispersed in 600 g ethanol, with the result that a 35 wt.-% dispersion formed. 100 ml of a solution of 0.5 g dimethyl 2,2′-azobis(2-methylpropionate) (trade name V 601; available from WAKO Chemicals GmbH, Fuggerstraβe 12, 41468 Neuss), 1 g methacryloxypropyltrimethoxysilane (MEMO) and 10 g trimethylolpropane trimethacrylate (TMPTMA) in white spirit was then added to the reaction mixture over 1 h. Stirring followed for a further 15 h at 75° C., the reaction mixture was filtered off, isolated as paste and dried under negative pressure.

Example	Metal	D50
9-1	Aluminum grit	1.6 μm
9-2	Copper grit	25 μm
9-3	Copper flakes	35 μm
9-4	Copper grit	9 μm
9-5	Tin grit	28 μm

The decomposition temperature of the polymer here was approx. 260° C., determined according to DIN EN ISO 11358. At this temperature, an incipient clear decrease in the weight of the powdered coating material was shown.

Example 10

Flame Spraying

10-1: Application of Examples 1 to 4

Using a flame spraying system from CASTOLIN, aluminum particles with a D₅₀ value of 2 μm without coating additive, as well as the aluminum particles according to Examples 1 to 4, were applied to a sheet by means of an oxy-acetylene flame. Furthermore, copper particles with a D₅₀ value of 34 μm without coating additive, as well as the copper particles according to Examples 5 to 8, were applied analogously. The obtained sheets were examined by means of SEM.

The sheets coated according to the invention were much more homogeneous in relation to their optics as well as their haptics. SEM photographs of the surfaces demonstrate the formation of larger uniform areas of the coating, while the surface of the comparison examples is characterized by a large number of isolated particles. Furthermore, the cross-section shows that cavities contained in the coating of the sheet according to the invention are significantly smaller.

10-2: Application of Examples 7-2 and 9-1

The aluminum particles according to Examples 7-2 and 9-1 were applied to steel sheets by means of a flame spraying system from CASTOLIN in an oxy-acetylene flame. The obtained sheets were then analyzed by means of SEM. A uniform coating was shown here, wherein small cavities and only negligible amounts of oxidation were observed. The coatings macroscopically showed a good adhesion to the steel sheets.

The application of aluminum particles according to Example 9-1 without coating additive did not allow a coating according to the invention. Only small quantities of greatly isolated, very coarse particulate particle agglomerates were applied to the surface here.

Example 11

Non-Thermal Plasma Spraying

The powdered coating material was applied by means of a Plasmatron system from Inocon, Attnang-Puchheim, Austria. Argon and nitrogen were used as ionizable gases. Standard process parameters were used here.

Examples 9-2 to 9-5 were applied to alu sheets, steel sheets and wafers. Here, a very uniform application of the powder, a small overspray, a good adhesion of the layer to the surface and a color of the coating which allows a small quantity of oxidation to be deduced were shown. This was also confirmed in subsequent SEM photographs. Examples of photographs of the coating with spherical copper grit according to Example 9-2 are found in FIGS. 1 and 2. For example the excellent binding to the surface is recognizable from FIG. 1. FIG. 2 shows the surprisingly uniform distribution of the individual particles in relation to the size of the individual particles (D₅₀=25 μm).

Attempts to apply particles without coating additive by means of non-thermal plasma spraying did not result in any usable coatings. In particular, no continuous coating could be achieved with this. Agglomerates occurring on the surface showed no noticeable binding to the substrate surface.

Claims

1. A process for producing a coating comprising:

introducing a particle-containing powdered coating material in a coating method selected from the group consisting of cold gas spraying, flame spraying, high-speed flame spraying, thermal plasma spraying and non-thermal plasma spraying, wherein the particles on the surface are at least partially covered with at least one coating additive which has a boiling point or decomposition temperature of below 500° C.

2. The process according to claim 1, wherein the weight proportion of the at least one coating additive is at least 0.01 wt.-%, relative to the total weight of the coating material and the coating additive.

3. The process according to claim 1, wherein the weight proportion of the at least one coating additive at most 80 wt.-%, relative to the total weight of the coating material and the coating additive.

4. The process according to claim 1, wherein the particles comprise metal particles, and the metal is selected from the group which consists of silver, gold, platinum, palladium, vanadium, chromium, manganese, cobalt, germanium, antimony, aluminum, zinc, tin, iron, copper, nickel, titanium, silicon, alloys and mixtures thereof.

5. The process according to claim 1, wherein the carbon content of the powdered coating material is from 0.01 wt.-% to 15 wt.-%, in each case relative to the total weight of the coating material and the coating additive.

6. The process according to claim 1, wherein the compounds used as coating additive has at least 6 carbon atoms.

7. The process according to claim 1, wherein the coating method is selected from the group consisting of flame spraying and non-thermal plasma spraying.

8. The process according to claim 1, wherein the at least one coating additive is selected from the group consisting of polymers, monomers, silanes, waxes, oxidized waxes, carboxylic acids, phosphonic acids, derivatives of the above-named and mixtures thereof.

9. The process according to claim 1, wherein the at least one coating additive comprises no is free of stearic acid and/or oleic acid.

10. The process according to claim 1, wherein the coating additive is applied mechanically to the particles.

11. The process according to claim 1, wherein the powdered coating material has a particle-size distribution with a D50 value from a range of from 1.5 to 53 μm.

12. A method for coating a substrate selected from the group consisting of cold gas spraying, flame spraying, high-speed flame spraying, thermal plasma spraying and non-thermal plasma spraying,

the method comprising

(a) introducing a particle-containing powdered coating material into a medium directed onto a substrate to be coated by cold gas spraying, flame spraying, high-speed flame spraying, thermal plasma spraying or non-thermal plasma spraying, wherein the particles are covered with at least one coating additive which has a boiling point or decomposition temperature of below 500° C.

13. The method according to claim 12, wherein the coating method is selected from the group consisting of flame spraying and non-thermal plasma spraying.

14. The method according to claim 12, wherein the powdered coating material is conveyed as an aerosol.

15. The method according to claim 12, wherein the medium directed onto the substrate is air or has been produced from air.

16. The process and according to claim 1, wherein the coating method is non-thermal plasma spraying.

17. The method according to claim 12, wherein the coating method is non-thermal plasma spraying.

18. The process according to claim 1, wherein the at least one coating additive comprises polymer(s), monomer(s), silane(s), wax(es), oxidized wax(es), carboxylic acid(s), phosphonic acid(s), derivatives of carboxylic acid(s), derivatives of phosphonic acid(s), or mixtures thereof.

19. The process according to claim 1, wherein the at least one coating additive comprises acrylate and/or methacrylate.

20. The process according to claim 1, wherein the at least one coating additive comprises organofunctional silane.

21. The process according to claim 1, wherein the weight proportion of carbon atoms in the powdered coating material ranges from 0.01 weight percent to 15 weight percent.