Methods for Substrate Coating and Use of Additive-Containing Powdered Coating Materials in Such Methods

Abstract

The present invention relates to the use of a particle-containing powdered coating material, wherein an additive has been at least partially applied to the surface of the particles, in coating methods, in particular 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 powdered coating materials for coating substrates. Furthermore, the present invention comprises methods for substrate coating using such 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 different 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.

A general problem of coating methods using a powdered coating material is the conveying of the powders. A very uniform feeding in of the powdered coating material is necessary in particular to produce particularly thin layers for example. For this reason, various specially designed conveyor devices are additionally to be found as the subject of separate patent applications. Examples are found in WO 03/029762 A1 and WO 2011/032807 A1.

The object of the present invention is to make it possible to produce novel coatings or to improve the production of known coatings. Furthermore, an object of the present invention is to make it possible to produce particularly thin coatings of high quality. Furthermore, an object of the present invention is to solve existing problems with respect to the conveyability of the powdered coating material used in a coating method.

A further object of the present invention is to provide methods for substrate coating which are characterized by novel coatings or an improved quality of the coating.

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 in a coating method, wherein the particles of the powdered coating material are at least partially provided with at least one additive and wherein the coating method is 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 additive or additives is at most 32 wt.-%, relative to the total weight of the coating material and the additive.

In particular embodiments of the above-named uses, the weight proportion of the additive or additives is between 0.02% and 32 wt.-%, in each case relative to the total weight of the coating material and the additive.

In particular embodiments of the above-named uses, the carbon content of the additive-containing particles 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 additive.

In particular embodiments of the above-named uses, the weight proportion of the additive or additives is at least 0.02 wt.-%, relative to the total weight of the coating material and the additive.

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

In particular embodiments of the above-named uses, the particles of the powdered coating material comprise or are metal particles, and 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 coating method is selected from the group consisting of flame spraying and non-thermal plasma spraying. Non-thermal plasma spraying is particularly preferred.

In particular embodiments of the above-named uses, the at least one 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 additive is, or the additives are, 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 powdered coating material has a span value in the range of from 0.4 to 2.9, which is defined as follows:

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

In particular embodiments of the above-named uses, the additive, or the additives, can be removed from the coated particles using organic and/or aqueous solvent.

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

In particular embodiments of the above-named uses, the powdered coating material has a particle-size distribution with a D₉₀ value in the range of from 9 to 103 μm.

In particular embodiments of the above-named uses, the powdered coating material has a particle-size distribution with a D₁₀ value in the range of from 0.2 to 5 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, wherein a powdered coating material is used the particles of which are provided at least partially with at least one additive.

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

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 above-named air can be taken from the surrounding atmosphere. In particular embodiments, in which for example a particularly high purity of the coating is desired, the air is purified before it is used, wherein for example dust and/or water vapor is separated off. It can likewise be preferred that the gaseous constituents of the air, other than nitrogen and oxygen, are also largely separated off completely, wherein the total amount of the impurities is preferably <0.01 vol.-%, further preferably <0.001 vol.-%.

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 provision of the surface of the particles of the powdered coating material with the additive, or the additives, need not be complete here in order to make the use according to the invention possible. Without being understood as limiting the invention, the inventors are of the view that the effect of the applied additives is caused, among other things, by an effect as spacers between the individual particles, wherein an application to or a coverage of the surface beyond a particular extent is not associated with a markedly improved conveyability, but requires an increased use of the additive, or the additives, which therefore only gives rise to costs and thus is not economically worthwhile. In particular embodiments, therefore, it is preferred that at most 90%, preferably at most 85%, more preferably at most 80%, still more preferably at most 75% and most preferably at most 70% of the surface of the particles is covered with the additive, or the additives. At the same time, however, as complete as possible a coverage of the surface of the particles provides a certain protective effect for example against oxidizing influences from the environment. In certain particularly preferred embodiments of the invention, therefore, it is preferred that at least 20%, preferably at least 25%, more preferably at least 30% and still more preferably at least 35% of the surface of the particles is covered with the additive, or the additives. In particular ones of the above-named embodiments, it is preferred in particular that at least 40%, preferably at least 50%, more preferably at least 55% and still more preferably at least 60% of the surface of the particles is covered with the additive, or the additives. A determination of the surface coverage of the powdered coating materials according to the invention is carried out by means of SEM, wherein 30 randomly selected particles are examined.

The inventors have surprisingly found that the conveyability of a powdered coating material is significantly increased by at least partially covering the surface of the particles with at least one additive. This is of great importance in coating methods, in particular in those in which a thin layer is to be applied, in order to obtain high-quality and reproducible results. An increase in the reproducibility of the method and more uniform feeding in of the powdered coating material furthermore makes it possible to produce much more homogeneous coatings with few defects and a very high degree of cross-linking of the particles. Such features are important in particular for the production of particularly thin coatings. In addition, a conveyability improved in this way results in a greatly simplified feeding in of the powdered coating material and a dramatic reduction in the outlay on equipment.

Methods according to the invention which can be used to build up coatings are for example cold gas spraying, thermal plasma spraying, non-thermal plasma spraying, flame spraying and high-speed flame spraying. An improved conveyability has proved to be of particularly great importance in particular in coating methods in which as low as possible a thermal load of the substrate is to be effected and no, or almost no, thermal component is used to apply the coating. In particular embodiments, therefore, the use of the powdered coating material according to the invention in flame spraying, non-thermal plasma spraying, cold gas spraying and high-speed flame spraying is preferred. In particular cases, it is desired in addition to be able also to coat delicate substrates with the method according to the invention, which is why the powdered coating material may be coated with only limited kinetic energy. In particular ones of the above-named embodiments, the method is therefore preferably selected from the group consisting of flame spraying and non-thermal plasma spraying. However, the industrial use of flame spraying requires the use and, to guarantee a continuous operation, the storage of large amounts of the gas used. As combustible gases are necessary to generate the flame in flame spraying, their storage is associated with a corresponding safety risk and therefore requires special safety regulations. A plasma, in contrast, can also be produced using non-combustible gases, with the result that the storage of corresponding amounts of gas is associated with lower safety standards and therefore reduced costs. In particular ones of the above-named embodiments, therefore, it is quite particularly preferred that non-thermal plasma spraying is used as coating method.

The term “additive” within the meaning of the present invention relates to substances which are present, not cross-linked, i.e. they have not been cross-linked, on the surface of the particles of the powdered coating material. In particular, the term “additive” relates, in preferred embodiments of the present invention, to carbon-containing compounds which have not been cross-linked on the surface of the particles of the powdered coating material. Within the meaning of the present invention, by “not cross-linked on the surface” is meant that no covalent bonds between the individual additive molecules are built up during or after the application of the additive to the particles of the powdered coating material, consequently no post-cross-linking takes place on the pigment surface. In particular, by the term “additive” is not meant cross-linked polymers such as are disclosed for example in EP 2115075 A1.

In particular embodiments, it is preferred in particular that the additives are only bound to the particles of the powdered coating material by means of physical bonds, for example by means of van der Waals interactions, dipole-dipole interactions or hydrogen bridges. However, it is also possible that the additives are additionally or alternatively bound to the surface of the particles of the powdered coating material by means of chemical bonds, such as for example covalent or ionic bonds.

In general, it is preferred that the additives according to the invention can be removed from the particles again through the use of organic and/or aqueous solvents. Such additives have in particular the advantage that they are easy and inexpensive to apply. In particular embodiments, particular preferred additives can be dispersed for example in a solvent and applied to the powder particles by mechanical forces. Additionally or alternatively, in particular embodiments, the additives can be dissolved in a suitable solvent, then mixed with the powder particles and applied by evaporation of the solvent onto the powder particles.

Without being understood as limiting the invention, the inventors are of the view that the additives according to the invention reduce the interactions between the particles and thereby increase the conveyability.

Substances which as additives within the meaning of the present invention are in particular carbon-containing compounds which are chemically and/or physically bound to the surface of the particles of the powdered coating material.

Without being understood as limiting the present invention, the inventors are of the view that a particularly strong improvement in the coatings produced according to the invention is brought about in the use of additives with a high carbon content in a combustion flame or a plasma flame by combusting the additive in the flame and applying agglomerates of the powdered coating material present here. In particular embodiments, therefore, it is preferred that the weight proportion of the carbon atoms in the additive-covered powdered coating material 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 additive-covered powdered coating material 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 and the additive.

On the other hand, in particular embodiments, it is preferred that the weight proportion of the carbon atoms in the additive-covered powdered coating material 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 and the additive.

In particular embodiments, it is preferred in particular that the weight proportion of the carbon atoms in the additive-covered powdered coating material lies in the range of between 0.01 wt.-% and 15 wt.-%, preferably in the range of between 0.05 wt.-% and 10 wt.-%, more preferably in the range of between 0.1 wt.-% and 7 wt.-% and still more preferably in the 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 additive-covered powdered coating material lies in the range of between 0.22 wt.-% and 4 wt.-%, preferably in the range of between 0.28 wt.-% and 3 wt.-%, more preferably in the range of between 0.34 wt.-% and 2 wt.-% and still more preferably in the range of between 0.4 wt.-% and 1 wt.-%. The above-named wt.-% are based on the total weight of the coating material and the additive. The weight proportion of the carbon atoms to the total weight of the coating material and the additive is determined for example with a CS 200 device from Leco Instruments GmbH.

In particular embodiments, furthermore, it is preferred that the compounds used as 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 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 additive according to the invention can be determined for example by determining the respective additive. All methods known to a person skilled in the art for determining a substance can be used here. For example, an 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 furthermore preferred that the weight proportion of the additive, or additives, 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 C content of the coating material and the 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 and the additive.

In further particular embodiments, it is furthermore preferred that the weight proportion of the additive is at most 32 wt.-%, preferably at most 18 wt.-%, more preferably at most 13 wt.-% and still more preferably at most 9 wt.-%. In particular ones of the above-named embodiments, it is preferred in particular that the C content of the coating material and the additive is at most 7 wt.-%, preferably at most 6 wt.-%, more preferably at most 4.5 wt.-% and still more preferably at most 2.3 wt.-%. The above-named wt.-% are based on the total weight of the coating material and the additive.

In further particular embodiments, it is furthermore preferred that the weight proportion of the additive lies in the range of between 0.02 wt.-% and 32 wt.-%, preferably in the range of between 0.08 wt.-% and 18 wt.-%, more preferably in the range of between 0.17 wt.-% and 13 wt.-% and still more preferably in the range of between 0.30 wt.-% and 9 wt.-%. In particular ones of the above-named embodiments, it is preferred in particular that the weight proportion of the carbon atoms in the coating material and the additive lies in the range of between 0.35 wt.-% and 7 wt.-%, preferably in the range of between 0.42 wt.-% and 6 wt.-%, more preferably in the range of between 0.54 wt.-% and 4.5 wt.-% and still more preferably in the range of between 0.62 wt.-% and 2.3 wt.-%. The above-named wt.-% are based on the total weight of the coating material and the additive.

Examples of substances which can be used as 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, phosphonic acids, phosphoric acid derivatives or mixtures thereof, are used as 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 preferably bound via physical bonds in particular embodiments. However, it is not ruled out that in further particular embodiments the waxes have functional groups which alternatively or additionally make 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 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 celluose, 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. Thermoplastic plastics are particularly preferred here, wherein all thermoplastics known to a person skilled in the art come into consideration. A summary of corresponding thermoplastics is found e.g. in the Kunststoff-Taschenbuch, ed. Saechtling, 25th edition, Hanser-Verlag, Munich, 1992, in particular chapter 4, 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 thermoplastics are to be named by way of example for illustration: polyoxyalkylenes, polycarbonates (PC), polyesters such as polybutylene terephthalate (PBT) or polyethylene terephthalate (PET), polyolefins such as polyethylene or polypropylene (PP), poly(meth)acrylates, polyamides, vinylaromatic (co)polymers such as polystyrene, impact-modified polystyrene such as HIPS, or ASA, ABS or AES polymers, polyarylene ethers such as polyphenylene ether (PPE), polysulfones, polyurethanes, polylactides, halogen-containing polymers, polymers containing imide groups, cellulose esters, silicone polymers and thermoplastic elastomers. Mixtures of different thermoplastics can also be used in the form of single- or multi-phase polymer blends.

Polyoxyalkylene homo- or copolymers, in particular (co)polyoxymethylenes (POM), and methods for the production thereof are known per se to a person skilled in the art and described in the literature. The polymer main chain of these polymers has at least 50 mol.-% recurring units of —CH₂O—. The homopolymers are generally produced, preferably catalytically, by polymerization of formaldehyde or trioxane. Polyoxymethylene copolymers and polyoxymethylene terpolymers are examples.

Suitable polycarbonates are known per se and can be obtained e.g. according to DE 1 300 266 B1 by means of interfacial polycondensation or according to DE 14 95 730 A1 by reacting biphenyl carbonate with bisphenols.

Suitable polyesters are also 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 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 ethylene-propylene elastomers and ethylene-propylene terpolymers.

Examples of the above-named poly(meth)acrylates 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.

The above-named polyamides also comprise polyetheramides such as polyether block amides and are described for example in the disclosures of 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. Furthermore, the above-named polyamides comprise for example polycaprolactams, polycapryllactams, polylaurolactams and polyamides, which are obtained by reacting dicarboxylic acids with diamines. Examples of dicarboxylic acids suitable for this are alkanedicarboxylic acids with 6 to 12, in particular 6 to 10 carbon atoms and aromatic dicarboxylic acids can be used. Examples of suitable diamines are 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 the above-named vinylaromatic (co)polymers are polystyrene, styrene-acrytnitrile copolymers (SAN) and impact-modified polystyrene (HIPS=High Impact Polystyrene). The production of such vinylaromatic (co)polymers is known to a person skilled in the art and is found for example in EP-A-302 485. Further examples are ASA, ABS and AES polymers (ASA=acrylonitrile-styrene-acrylester, ABS=acrylonitrile-butadiene-styrene, AES=acrylonitrile-EPDM rubber-styrene). The production of ABS polymers is found for example in DE 197 28 629 A1 and the production of ASA polymers is found for example in EP 99 532 A2. Details on the production of AES polymers is furthermore found for example in U.S. Pat. No. 3,055,859 or in U.S. Pat. No. 4,224,419.

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 thereof can be the same or different, and independently of each other can be for example an aromatic radical with 6 to 18 C atoms. Examples of suitable arylene radicals are phenylene, bisphenylene, terphenylene, 1,5-naphthylene, 1,6-naphthylene, 1,5-anthrylene, 9,10-anthrylene or 2,6-anthrylene. Examples of production details for polyarylene ether sulfones are found in EP 113 112 A1 and EP 135 130 A2.

Further examples of plastics which can be used as additives in particular embodiments are polyurethanes, polyisocyanurates and polyureas.

Examples of the polymers of lactic acid, polylactides, as well as methods for the production thereof are known to a person skilled in the art. In particular embodiments, it is preferred in particular to use copolymers or block copolymers based on lactic acid and further monomers.

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

Further examples of plastics which can be used as additives in particular embodiments are 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).

Examples of the above-named 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.

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, 2nd 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-o×y 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 vulcanisates (TPE-V).

Examples of the above-named polyacrylates are poly(meth)acrylates, which are preferably present as homopolymers or as block polymers. Such polymers are sold for example by Evonik under the trade name Degalan.

In particular embodiments, it is preferred that the additives are selected from the group consisting of the products of the copolymerization of PE or PP with maleic acid (anhydride) or acrylic acid.

In particular embodiments, it is preferred that the polymers used as 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 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 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 additives comprise no stearic acid 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. 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 (wherein the nitrogen atom is optionally, independently of each other, substituted once or twice with C1-C5 alkyl or aryl groups), ureido (wherein the nitrogen atoms is 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 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 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 additives used according to the invention carry no functional groups. 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 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 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.

The inventors have surprisingly found that when the powdered coating materials covered with an additive according to the invention are used, the use of coating materials with an unexpectedly high melting point also allowed. 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 particles to strike the substrate surface individually 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 apparently 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 uniformly fed-in particles without agglomerates.

For example, in particular embodiments, according to the invention powdered coating materials covered with at least one 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 according to the invention powdered coating materials covered with at least one 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 term “homogeneous layer” within the meaning of the present invention describes that the relevant coating has 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 produced according to the invention, wherein for example a length of 100 μm of the substrate coating is examined.

It was surprisingly found that not only is there an improved conveyability of powdered coating materials through the use of the coating material and the additive, but even previously unconveyable powdered coating materials can be conveyed easily and can be used to produce high-quality coatings.

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 manufacturer's 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 in the range of from 1.5 to 53 μm, preferably in the range of from 2 to 51 μm, more preferably in the range of from 4 to 50 μm and still more preferably in the 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 in the range of from 7 to 48 μm, preferably in the range of from 9 to 47 μm, more preferably in the range of from 11 to 46 μm and still more preferably in the 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 in the range of from 1.5 to 45 μm, preferably in the range of from 2 to 43 μm, more preferably in the range of from 2.5 to 41 μm and still more preferably in the 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 in the range of from 3.5 to 38 μm, preferably in the range of from 4 to 36 μm, more preferably in the range of from 4.5 to 34 μm and still more preferably in the 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 in the range of from 9 to 53 μm, preferably in the range of from 12 to 51 μm, more preferably in the range of from 15 to 50 μm, still more preferably in the 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 in the range of from 19 to 48 μm, preferably in the range of from 21 to 47 μm, more preferably in the range of from 23 to 46 μm and still more preferably in the 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 in the range of from 42 to 103 μm, preferably in the range of from 45 to 99 μm, more preferably in the range of from 48 to 95 μm and still more preferably in the 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 in the range of from 52 to 87 μm, preferably in the range of from 54 to 81 μm, more preferably in the range of from 56 to 75 μm and still more preferably in the range of from 57 to 71 μm.

Furthermore, it was surprisingly found that a clear improvement in the conveyability of fine particle sizes is achieved by an additive covering. This provides the advantage that powdered coating materials with a larger proportion of fines and therefore better activatability in non-thermal plasma spraying can also be used. In further particular embodiments of the invention, 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 additive-covered powdered coating materials 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 additive-covered, powdered coating material 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 additive-covered, powdered coating material 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 additive-covered, powdered coating material is characterized in that it have a particle-size distribution with a D₁₀ value from a range of from 0.2 to 5 μm, preferably from a range of from 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 additive-covered, powdered coating material 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 additive-covered, powdered coating material 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 in the range of from 0.4 to 2.9, preferably in the range of from 0.5 to 2.6, more preferably in the range of from 0.6 to 2.4 and still more preferably in the 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 in the range of from 0.8 to 1.9, preferably in the range of from 0.9 to 1.8, more preferably in the range of from 1.0 to 1.7 and still more preferably in the 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. For example, in particular preferred embodiments the powdered coating material has a particle-size distribution with a span in the range of from 0.4 to 2.9 and a D₅₀ value in the range of from 1.5 to 53 μm, preferably in the range of from 2 to 51 μm, more preferably in the range of from 4 to 50 μm, still more preferably in the range of from 6 to 49 μm and most preferably in the 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 in the range of from 0.5 to 2.6 and a D₅₀ value in the range of from 1.5 to 53 μm, preferably in the range of from 2 to 51 μm, more preferably in the range of from 4 to 50 μm, still more preferably in the range of from 6 to 49 μm and most preferably in the range of from 7 to 48 μm. In particular further preferred embodiments, the powdered coating material has a particle-size distribution with a span in the range of from 0.6 to 2.4 and a D₅₀ value in the range of from 1.5 to 53 μm, preferably in the range of from 2 to 51 μm, more preferably in the range of from 4 to 50 μm, still more preferably in the range of from 6 to 49 μm and most preferably in the 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 in the range of from 0.7 to 2.1 and a D₅₀ value in the range of from 1.5 to 53 μm, preferably in the range of from 2 to 51 μm, more preferably in the range of from 4 to 50 μm, still more preferably in the range of from 6 to 49 μm and most preferably in the 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_O is the upper span value, p_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 a 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 lies 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 K 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 spraying 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 provided with a coating before they were covered with the additive.

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 metal sheets 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 provided 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, semi-conductive 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 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 wafer, coated with solar contact paste, which has been coated with a powdered coating material according to the invention using non-thermal plasma spraying according to Example 14.

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 Acrylic Polymer (Poly(Isobutyl Methacrylate)

0.3 g of an acrylic polymer based on isobutyl methacrylate (Degalan P 675, from Evonik) was used as additive and dissolved in 50 g ethyl acetate. This mixture was then introduced, together with 240 g aluminum particles (D₅₀=17.5 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 additive-containing particles were removed from the kneader and then screened (71 μm).

Example 2

Powdered Coating Materials Covered with Ethyl Cellulose

The application of the additive was carried out analogously to Example 1. 1 g ethyl cellulose (Ethocel Standard 10, from Dow Wolff Cellulosics) was used as additive.

Example 3

Powdered Coating Materials Covered with Acrylic Polymer (Methyl Methacrylate)

The application of the additive was carried out analogously to Example 1. 2 g of an acrylic polymer based on methyl methacrylate and n-butyl methacrylate (Degalan LP AL 23, from Evonik) was used as additive.

Example 4

Powdered Coating Materials Covered with 1,10-Decanedicarboxylic Acid

3 g of 1,10-decanedicarboxylic acid was used as coating excipient 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 excipient were removed from the kneader and then screened (71 μm).

Example 5

Powdered Coating Materials Covered with Monoethyl Fumarate

The application of the coating excipient was carried out analogously to Example 4. 3 g monoethyl fumarate was used as coating excipient.

Example 6

Powdered Coating Materials Covered with Adipic Acid Monoethyl Ester

The application of the coating excipient was carried out analogously to Example 4. 3 g adipic acid monoethyl ester was used as coating excipient.

Example 7

Powdered Coating Materials Covered with Methyl Triglycol

The application of the coating excipient was carried out analogously to Example 4. 3 g methyl triglycol was used as coating excipient.

Example 8

Powdered Coating Materials Covered with Adipic Acid Monoethyl Ester

The application of the coating excipient was carried out analogously to Example 4. However, copper particles with a D₅₀ of 34 μm were used here. 3 g adipic acid monoethyl ester was used as coating excipient.

Example 9

Powdered Coating Materials Covered with Methyl Triglycol

The application of the coating excipient was carried out analogously to Example 4. However, a copper particle with a D₅₀ of 34 μm was used here. 3 g methyl triglycol was used as coating excipient.

Example 10

Powdered Coating Materials Covered with Ethocel

The application of the coating excipient was carried out analogously to Example 4. A copper particle with a D₅₀ value of 34 μm was used here. 3 g ethyl cellulose (Ethocel Standard 10, from Dow Wolff Cellulosics) was used as coating excipient.

Example 11

Powdered Coating Materials Covered with Monoethyl Fumarate

The application of the coating excipient was carried out analogously to Example 4. 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 excipient.

Example 12

Powdered Coating Materials Covered with Aerosil 200

The additive was applied analogously to Example 4. 100 g spherical tin particles with a D₅₀ of 28 μm were used here. 3 g Aerosil 200 (pyrogenic silicic acid, from Evonik) was used as additive.

Example 13

Determination of the Conveyability

In order to determine an improvement in the conveyability of the powdered coating material covered with an additive according to the invention, an AS 100 fluidimeter from Sames was used. There, 250 g of the respective particles according to Examples 1 to 3 were poured in and fluidized with a gas. Nitrogen was used here as gas. A calibrated bore was then opened for 30 seconds and the weight (W) of the material that flowed out in this time was recorded as the measured variable.

Sample                  Weight
Standard alu grit WA 25 5 g
Example 1               12 g
Example 2               28 g
Example 3               16 g

Example 14

Non-Thermal Plasma Spraying of Tin Particles

The powdered coating material was applied by means of a Plasmatron system from Inocon, Attnang-Puchheim, Austria. Nitrogen was used as ionizable gas. Standard process parameters were used here. Wafers coated with a solar contact paste were used as substrate. Additive-covered tin particles according to Example 12 and analogous tin particles without additive served as powdered coating materials.

The conveying of the tin particles without additive was not possible in the consistency required for the coating. The conveying failed rapidly and the small amount conveyed was apparently fed into the flame intermittently. In contrast, the powdered coating material according to Example 12 was able to be conveyed without trouble and a first visual evaluation of the obtained coatings showed a uniform application. SEM photographs of the obtained coatings are found in FIGS. 1 and 2.

Example 15

Flame Spraying of Powdered Coating Materials According to Examples 4 to 11

Using a flame spraying system from CASTOLIN, aluminum particles with a D₅₀ value of 2 μm without coating excipient, as well as the aluminum particles according to Examples 4 to 7, were applied to a metal sheet by means of an oxyacetylene flame. Furthermore, copper particles with a D₅₀ value of 34 μm without coating excipient, as well as the copper particles according to Examples 8 to 11, were applied analogously. The obtained metal sheets were examined by means of SEM.

The metal 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 metal sheet according to the invention are significantly smaller.

Claims

1. A process for producing a coating, comprising:

introducing a particle-containing powdered coating material into 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 of the powdered coating material comprise at least one additive.

2. The process according to claim 1, wherein the weight proportion of the at least one additive is at most 32 wt.-%, relative to the total weight of the coating material and the additive.

3. The process according to claim 1, wherein the carbon content of the powdered coating material comprising the at least one additive is from 0.01 wt.-% to 15 wt.-%, relative to the total weight of the coating material and the additive.

4. The process according to claim 1, wherein the weight proportion of the at least one additive is at least 0.02 wt.-%, relative to the total weight of the coating material and the at least one additive.

5. The process according to claim 1, wherein the at least one additive has at least 6 carbon atoms.

6. The process according to claim 1, wherein the particles comprise metal particles, and 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.

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 additive is free of stearic acid and/or oleic acid.

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

10. The process according to claim 1, wherein the at least one additive can be removed from the coated particles using organic and/or aqueous solvent.

11. The process according to claim 1, wherein the powdered coating material has a particle-size distribution with a D50 value ranging 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 comprise least one additive; and

(b) depositing the powdered coating material onto the substrate.

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 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 of claim 9, wherein the waxes comprise natural waxes and synthetic waxes.

19. The process of claim 1, wherein the powdered coating material has a span value according to formula I Span = D 90 - D 10 D 50 ( I )

in the range of from 0.4 to 2.9.

20. The process of claim 1, wherein at most 70% of the surface of the particles of the powdered coating material is covered with the additive.

21. A coating produced according to the process of claim 1.

22. A coated substrate produced according to the method of claim 12.