Aqueous coating composition and use thereof

Abstract

To provide a coating composition which permits precise setting of the coefficients of friction of components, and which moreover manages without the use of PTFE and preferably dispenses entirely with fluorinated polymers.SOLUTION: The invention relates to a coating composition for producing a coating with an adjustable coefficient of friction.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to the field of coatings technology, in particular to coatings for high volume bulk materials. In particular, the present invention relates to an aqueous coating composition for the production of a coating having an adjustable coefficient of friction. Furthermore, the present invention relates to a method for the production of a coating having an adjustable coefficient of friction and to the use of the aqueous coating composition for the production of a coating having an adjustable coefficient of friction. Finally, the present invention relates to a coated substrate. [Background technology]

[0002] Fasteners, especially small parts such as bolts, nuts and screws, which are used for the mechanical fastening of parts, especially metal parts, need to have a specific and reproducible coefficient of friction so that they can be processed industrially. The coefficient of friction μ, also known as the frictional coefficient, indicates the ratio of the frictional force to the normal force; the higher the coefficient of friction, the higher the frictional force. The higher the frictional force, the less energy is required for the thread to stretch elastically or cathodically during the tightening process, and the so-called preload force is reduced. Preload forces are usually specified to ensure reliable performance of bolted joints, and for that reason the coefficient of friction must move within a defined range. This is particularly important when fastening materials, including bolts, screws, nuts, or even rivets, since they are used for a purely mechanical fastening of parts. On the one hand, friction must be high enough to prevent unintentional loosening of the composite, but at the same time low enough to allow a perfect material-material bond. In addition, the coefficient of friction must be set as constant as possible to allow industrial, especially robotic, processing, for example for screws with a defined torque or bolt rivets with always the same strength. For this reason, small fastening parts are often coated in practice with special coating compositions in the form of a top coat, which are intended to set and influence the sliding and frictional properties of the parts in a desired way.

[0003] The desired sliding and friction properties for screws or bolts are usually determined in accordance with DIN EN ISO 16047:2013-01, where a coefficient of friction μ in the window of 0.09 to 0.16 is specified specifically for screws by the German Automotive Manufacturers Association (VDA). To set the desired coefficient of friction, certain topcoat compositions usually contain fluorinated plastic particles, particularly polyfluorotetraethylene (PTFE) or polyvinylidene fluoride (PVDF) based particles. However, the use of over- or partially fluorinated compounds has some serious drawbacks. On the one hand, fluoropolymers are relatively expensive, and on the other hand, they should be avoided from the viewpoint of environmental protection. During the production of fluorinated compounds, especially PTFE, significant amounts of perfluorooctanoic acid (PFOA) are usually produced or used for the production of these compounds. Perfluorooctanoic acid is practically not naturally degraded, accumulates in the body, and is particularly liver-damaging, reproductively toxic, and carcinogenic. The production of perfluorooctanoic acid and its precursor compounds has therefore been banned in the European Union since July 4, 2020, with few exceptions. In addition, the manufacture or use of PTFE also generates polyfluorinated by-products and decomposition products, which should not be released into the environment if possible. For these reasons, efforts are being made to replace polyfluorinated plastics by other materials whenever possible, but such a replacement is often not easy, since polyfluorinated or perfluorinated plastics have special and sometimes outstanding physical properties, in particular in terms of hydrophobic wetting or non-wetting properties, resistance to chemical and physical influences, and good sliding properties.

[0004] One of the problems that arise especially in threaded connections is the heat release behavior, since the sliding properties of many plastics change at high temperatures. In particular, the sliding properties of many plastics improve when heated. However, this is undesirable in threaded connections, since there is otherwise a risk of unintentional loosening of the connection. Perfluorinated plastics, especially PTFE and PVDF, do not exhibit such problematic behavior or only to a limited extent, so they are still today the materials of choice for setting the sliding or friction properties of fasteners in a targeted manner. PTFE is characterized by a particularly high melting point, which makes it possible to optimize the friction behavior in the high temperature range. Another problem that occurs especially when screws are tightened at high speeds is the so-called stick-slip effect. In this case, the screw does not move smoothly during tightening, but instead starts to stick or slip. This leads to torque uncertainty on the one hand and preload uncertainty on the other hand, which can then lead to potential risks of failure during operation. The stick-slip effect must therefore be avoided as far as possible, which is why the slip and adhesion properties of the bolts must be set particularly precisely and uniformly. At present, the stick-slip effect can only be largely prevented by using topcoats containing fluoropolymers. However, one of the disadvantages of fluoropolymers is that they are hydrophobic and should therefore be used preferentially in solvent-based systems, although for environmental and occupational safety reasons water-based systems are increasingly preferred. Another problem is that even when fluoropolymer topcoats are used, the coefficient of friction values ​​are often subject to wide variations, i.e., the coefficients of friction for individual screws coated with the same topcoat vary widely from one another. In this case, a topcoat that limits the spread in coefficient of friction values ​​to a smaller range is desirable to further increase the quality of the bolted joint. Summary of the Invention

[0005] To date, the state of the art has lacked a water-based coating system that allows the coefficient of friction of small fasteners to be specifically targeted and controlled without fluoropolymers, preferably completely without fluoropolymers, and does so while meeting the requirements regarding narrowly defined coefficient of friction window, heat release and stick-slip behavior. It is therefore one of the objects of the present invention to provide a coating composition which allows the coefficient of friction of parts, in particular fastening parts such as screws, nuts, bolts or rivets, to be precisely set and even controlled without the use of PTFE, preferably completely eliminating the need for fluoropolymers. It is further an object of the present invention to provide a coating system that is free of at least significant amounts of organic solvents, and preferably free of organic solvents. It is a further object of the present invention to provide a coating system which largely prevents the stick-slip effect. Finally, it is an object of the present invention to minimize variability in the coefficient of friction. Thus, a subject of the present invention according to a first aspect is an aqueous coating composition according to claim 1. Further advantageous embodiments of this aspect of the invention are the subject of the associated dependent claims. Furthermore, another subject of the invention according to a second aspect is the use of a coating composition according to claim 13. A further subject of the invention according to a third aspect thereof is a method for producing a coating according to claim 14. Further advantageous embodiments of this aspect of the invention are subject of the associated dependent claims. Finally, a further subject of the invention according to a fourth aspect is a metal substrate according to claim 16. Further advantageous embodiments of this aspect of the invention are the subject of the associated dependent claims.

[0006] It will be appreciated that certain characteristics, features, embodiments, advantages, etc., which are set forth below with respect to only one aspect of the invention (so as to avoid unnecessary repetition), naturally apply as appropriate with respect to other aspects of the invention without the need for explicit mention. In addition, it applies that all values ​​or parameter data etc. mentioned below can in principle be determined or can be determined by standardized or clearly stated determination methods or by determination methods well known to those skilled in the art. Further, it will be understood that all weight or amount related percentages will be selected by one of ordinary skill in the art such that the totals add up to 100%. Given the above, the invention will now be described in more detail. The drawings show: [Brief description of the drawings]

[0007] [Figure 1] 1 is a listing of the coefficient of friction for threads coated with a zinc flake coating and then a topcoat of the present invention. [Diagram 2] Listing of coefficients of friction for threads coated with zinc flake coating and a commercial PTFE-containing topcoat. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Thus, a subject of the present invention is - according to a first aspect of the invention - an aqueous coating composition for producing a coating, in particular a topcoat, with an adjustable coefficient of friction, said composition comprising: (a) Organic and / or inorganic binders (b) a lubricant in an amount of at least 1.3 wt. % based on said coating composition; and (c) Platelet-shaped particles As the applicant has surprisingly found, aqueous coating compositions for topcoats with clearly adjustable coefficients of friction can be obtained based on commercially available organic or inorganic binders when at least one defined amount of lubricant and platelet-shaped particles are added to said compositions. Particularly good results are obtained when using a mixture of organic and inorganic binders. The compositions of the present invention are particularly free of fluoropolymers, in particular PTFE. Surprisingly, the coating compositions of the present invention, after curing to said topcoat, exhibit sliding and friction properties comparable to PTFE-containing topcoat compositions, but the variability in measured coefficient of friction of coated fasteners, such as screws, is significantly lower than fluorinated, especially PTFE-containing, coating compositions previously used in the prior art.

[0009] Moreover, the topcoat system of the present invention shows a consistent coefficient of friction even under high temperatures, especially high drying temperatures. This is surprising because lubricant-containing topcoats, especially when they contain wax, have a higher coefficient of friction after exposure to temperature. In particular, this is a result of the fact that the lubricant, especially wax, passes into the gas phase or thermally decomposes during the drying process. Surprisingly, topcoats that contain platelet-shaped particles in addition to lubricants do not show such an increase in coefficient of friction. Without wishing to be bound by theory, this is probably a result of the fact that the platelet-shaped particles act as a diffusion barrier, slowing the penetration of oxygen into the coating and thus slowing the decomposition of the lubricant, while preventing the lubricant from passing into the gas phase when using volatile or sublimable lubricants. The coating composition of the invention thus makes it possible to set the coefficient of friction much more precisely, with significantly lower fluctuations, than the PTFE-containing topcoat compositions used to date. This effect is particularly evident when using mixtures of organic and inorganic binders, especially when the organic binder is based on an acrylate-based binder, i.e., on acrylic or polyacrylate or copolymers thereof (acrylates being preferred), and when, as explained below, the inorganic binder is a silicon-containing binder. The coating compositions of the present invention can be easily formulated in aqueous media and may further be free of PTFE.Preferably, they may be completely free of fluoropolymers. The present invention therefore allows the easy use of topcoats that can set the coefficient of friction to the values ​​required for industrial production in both solvent- and fluoropolymer-free, particularly PTFE-free, systems. The coating composition of the present invention is therefore superior both from an environmental and occupational safety standpoint to the usual fluoropolymer-containing solvent-based systems known to date. In addition, substrates coated with the coating composition of the present invention, particularly fastening means such as screws, nuts, bolts, etc., show significantly lower variations in the coefficient of friction than the PTFE-containing systems used to date. It has been found that when lubricants and platelet-shaped pigments are added to the binder, the sliding properties improve significantly and the coefficient of friction can be set stable, even at high temperatures, in particular.

[0010] In the context of the present invention, lubricants are understood to mean chemical substances or mixtures of substances that modify the tribological properties of the coating, in particular that reduce friction. In the context of the present invention, lubricants can be present either in liquid or solid form, whereby the use of solid lubricants is preferred. In the context of the present invention, waxes are understood as substances, in particular natural or artificially obtained, that are usually kneadable at 20°C, solid to brittle and hard, coarse to fine crystalline, translucent to opaque but not glassy, ​​and melt above 40°C without decomposition. Above their melting point, even slightly, waxes usually have a relatively low viscosity and are not stringy. Waxes differ from similar synthetic or natural products mainly in that they usually change into a molten, low-viscosity state between about 50 and 90°C, exceptionally up to about 200°C, and are substantially free of ash-forming compounds. Waxes form pastes or gels and usually burn with a sooting flame. Depending on their origin, waxes are divided into three groups: natural waxes, semi-synthetic waxes and synthetic waxes. Natural waxes consist in particular of vegetable waxes such as candelilla wax, carnauba wax or montan wax, animal waxes such as beeswax, lanolin and brushing oil, mineral waxes such as ceresin and ozokerite, and petrochemical waxes such as petrolatum, kerosene wax and microwax. Semi-synthetic waxes are in particular hard waxes such as montan ester waxes and hydrogenated jojoba wax. Synthetic waxes are, for example, polyalkylene waxes or polyethylene glycol waxes.

[0011] In the context of the present invention, platelet-shaped particles, often also called flake-like particles, are understood as particles whose thickness is much smaller than their length and width, i.e. whose extent in one spatial direction is much smaller than in the other two spatial directions. Usually, the aspect ratio, i.e. the ratio of the particle length or width to the particle thickness, is in the range of 2:1 to 100:1, in particular 4:1 to 50:1, preferably 5:1 to 20:1, preferably 8:1 to 15:1. As mentioned above, in industrial production, especially in robotic screw tightening, it is essential that the sliding properties or coefficient of friction of coated fasteners, especially screws, always assume comparable values ​​in a reproducible manner. For this reason, VDA guideline 235-101 specifies so-called friction coefficient windows in which the coefficient of friction μ of fastening means, especially bolts, nuts and screws, can be located. This friction coefficient window covers a range of friction coefficient μ from 0.09 to 0.16. The friction coefficient is determined in accordance with DIN EN ISO 16047:2013-01. If other friction coefficient windows are specified and desired, these can also be met by the invention described herein.

[0012] Within the scope of the present invention, it is preferred if the surfaces or coated substrates coated with the coating compositions of the present invention have a coefficient of friction μ, determined according to DIN EN ISO 16047:2013-01, in the range of 0.09 to 0.16. In the case of a screw, the coefficient of friction is determined both on the thread and on flat surfaces, especially on the head of the screw. This double determination is necessary because the workpiece, especially the threaded component, has a different coefficient of friction on the thread than on flat coated surfaces, such as the head of the screw. For example, a screw designed as an internal support has a higher coefficient of friction on the thread than on the head of the screw on the nut or washer of the screw, and therefore has poorer sliding properties. If the screw is an external support, the coefficient of friction is higher on the head than on the thread. Because determining the coefficient of friction of the entire workpiece involves measuring the coefficient of friction of both areas (threads and flat surfaces), workpieces coated with lubricant-free coatings often have an undesirably high coefficient of friction, necessitating the use of additional lubricant, for example, during the bonding process. However, in accordance with the present invention, the use of lubricant can be omitted. Within the scope of the present invention, it is preferably provided that for threaded parts, e.g. screws, the coefficients of friction of both the thread and the flat surface lie within the above-mentioned friction coefficient window of a coefficient of friction μ of 0.09 to 0.16, respectively.

[0013] Since the test rules described in DIN EN ISO 16047:2013-01 apply to single fastenings, the test arrangements for multiple fastenings are further specified in the test sheets according to VDA 235-203. Within the scope of the present invention, it is preferably further provided that the above-mentioned friction coefficient window for the coefficient of friction μ of 0.09 to 0.16 is also met in the case of multiple tightenings both on threads and on flat surfaces. In addition, the thermal loosening behavior of workpieces, especially fasteners such as screws or bolts, is also important, especially when they are installed in assemblies, for example close to the engine. For this reason, VDA test sheet 235-203 specifies the preparation of tests with temperature load at 150°C, where the coefficient of friction μ of 0.06 must not be undershoot. Within the scope of the present invention, it is therefore preferred if the workpiece coated with the coating composition of the present invention has a coefficient of friction μ of 0.06 or more at 150° C. according to VDA test sheet 235-203. This coefficient of friction window is preferably filled for both the total coefficient of friction and, in the case of a threaded workpiece, for both the thread and the flat surface. As disclosed above, the coating composition of the present invention comprises a binder. The amount of the binder that the coating composition comprises can vary within a wide range according to the exact requirements and the respective intended application. Typically, however, the coating composition comprises the binder in an amount of 6 to 40 wt.%, in particular 9 to 33 wt.%, preferably 11 to 27 wt.%, more preferably 13 to 22 wt.%, based on the coating composition.

[0014] As before, the binder may be selected from organic binders, inorganic binders, and mixtures thereof. Preferably, the coating composition contains at least one organic binder. Still further in the context of the present invention, it is preferred that the coating composition contains an organic binder and an inorganic binder. Thus, in the context of the present invention, it is preferred that the coating composition contains a mixture of organic and inorganic binders. When the coating composition comprises an organic and an inorganic binder, the coating composition may comprise the organic binder in virtually any amount, but it is well documented when the coating composition comprises the organic binder in an amount of 2 to 20 wt.%, in particular 3 to 15 wt.%, preferably 4 to 12 wt.%, more preferably 5 to 10 wt.%, based on the coating composition. The coating composition preferably comprises an inorganic binder in addition to the organic binder. The addition of an inorganic binder increases, in particular, the abrasion resistance and mechanical durability of the coating. In addition, the use of inorganic coatings is also commercially desirable, since they are often cheap to produce or obtain on a large industrial scale. When the coating composition comprises an organic and an inorganic binder, it is well documented if the coating composition comprises the inorganic binder in an amount of 4 to 20 wt.%, in particular 6 to 18 wt.%, preferably 7 to 15 wt.%, more preferably 8 to 13 wt.%, based on the coating composition.

[0015] Turning now to the organic binder, this can be selected from a variety of suitable binders. Typically, the organic binder comprises or consists of an organic polymer, preferably, the organic binder consists of an organic polymer. The organic polymer may be selected from the group consisting of acrylates, polyurethanes, polyvinyl acetates, and mixtures and copolymers thereof. Preferably, the polymer is selected from the group consisting of acrylates, polyurethanes, and mixtures and copolymers thereof, in particular acrylates and copolymers of actylate. In the context of the present invention, particularly good results are obtained when the polymer is an acrylate. In the context of the present invention, organic binders based on acrylates, particularly pure acrylates, are thus preferably used, often also called polyacrylates or acrylics. Acrylates or polyacrylates or acrylics are polymers of acrylic or methacrylic acid or their esters. Acrylic binders are easily formulated, especially in aqueous media, and have excellent film-forming properties.

[0016] In the context of the present invention, therefore, the polymer is a copolymer of acrylic acid, acrylic acid and C1- to C 10 -Esters with alcohols, methacrylic acid, methacrylic acid and C1-C 10 It has been well documented that the polymers can be obtained from monomers selected from the group consisting of acrylic acid, esters of acrylic acid with C1- to C2-alcohols, fumaric acid, maleic acid, and mixtures thereof. 10 - ethers with alcohols, methacrylic acid, and methacrylic acid with C1- to C 10 Particularly good results are obtained when the monomer can be obtained from a monomer selected from the group consisting of esters with .alpha.- and .alpha.-alcohols, and mixtures thereof. It is further preferred in the context of the present invention if the polymer is obtainable from a monomer selected from the group consisting of acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate and hexyl methacrylate. In this context, it is particularly well documented if the polymer is obtainable from a monomer selected from the group consisting of acrylic acid, methyl acrylate, ethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate and mixtures thereof, preferably acrylic acid, methacrylic acid and mixtures thereof.

[0017] As far as the molecular weight of the polymer is concerned, this can of course vary over a wide range, but it is well documented when the polymer has a weight-average molecular weight Mw in the range of 2,000 to 250,000 g / mol, in particular 5,000 to 200,000 g / mol, preferably 10,000 to 150,000 g / mol and more preferably 15,000 to 100,000 g / mol. The molecular weight of the polymeric compounds given in the context of the present invention refers to the weight-average molecular weight Mw, which is the weight of the individual polymeric compounds weighted by their mass fractions. The molecular weight or molecular weight distribution can be determined by various standardized procedures and methods, such as light scattering, rheology, mass spectrometry, permeation chromatography, etc. However, the methods used to determine the molecular weight distribution are well known to those skilled in the art and do not require further explanation. For example, the molecular weight of the polymers used can be determined, in particular, by GPC methods, in particular according to DIN 55672, with polymethyl methacrylate or polystyrene as standards.

[0018] The inorganic binder is usually a silicon-containing binder. Preferably, the organic binder is selected from silanes, silane hydrolysates, silicates, polysiliconates, and mixtures thereof. In this connection, particularly good results are obtained when the inorganic binder is selected from the group of silanes, such as, in particular, trialkoxysilanes and tetraalkoxysilanes, preferably vinylsilanes, aminesilanes, phenoxysilanes and / or epoxysilanes, tetraethylorthosilicate (TEOS), tetramethylorthosilicate (TMOS), silane hydrolysates, colloidal silicic acid, water glass or silicates, in particular lithium water glass, sodium water glass, potassium water glass and mixtures thereof. In particular, silanes that can be preferably used are those mentioned below for the preparation of silane-modified silicates. According to a preferred embodiment of the present invention, the inorganic binder is in particular free of lithium compounds. In the context of the present invention, particularly good coating and sliding properties can be obtained when lithium polysilicate (lithium water glass), which is usually preferred, is not used. This is a notable advantage of the present invention, since the demand for lithium and the subsequent price of lithium are expected to increase due to the increasing use of lithium-ion batteries and lithium-ion accumulators, especially in the automotive field. Preferably, the inorganic binder is selected from the group of silanes, in particular trialkoxysilanes and tetraalkoxysilanes, preferably vinylsilanes, aminesilanes, phenoxysilanes and / or epoxysilanes, tetraethylorthosilicate (TEOS), tetramethylorthosilicate (TMOS), silane hydrolysates, colloidal silicic acid (silica sol), sodium water glass, potassium water glass and mixtures thereof. More preferably, the inorganic binder is selected from the group of sodium water glass, potassium water glass and mixtures thereof.

[0019] According to a more preferred embodiment of the invention, the inorganic binder contains or consists of a mixture of water glass and / or colloidal silicic acid with silane hydrolysates and / or silanes. Preferably, the inorganic binder contains a mixture of water glass and / or colloidal silicic acid with silane hydrolysates and / or silanes. These mixtures also do not show carbonation at alkaline pH values. According to this embodiment, it is preferred if the organic binder comprises the water glass and / or the colloidal silicic acid in a weight ratio in the range of 15:1 to 1:2, in particular 1:1 to 1:1.5, preferably 5:1 to 1:1, more preferably 4:1 to 1:1 relative to the silane hydrolysate and / or silane. Likewise, according to this embodiment, it has been well documented if the inorganic binder, in particular before mixing with the organic binder, is set to a pH of less than 11, in particular less than 9, preferably less than 8.5. Preferably, the inorganic binder, in particular before mixing with the organic binder, is set to a pH value of less than 8, in particular in the range from pH 5 to pH 7.5. In mixtures of water glass and / or colloidal silicic acid with silane hydrolysates and / or silanes, a rather weak or low carbonation, i.e. the absorption of carbon dioxide from the air and the subsequent formation of carbonates, is observed, especially at pH values ​​in the alkaline range. Carbonation leads to an undesirable deterioration of the surface properties, especially the appearance, especially in the case of topcoats, due to the turbidity of the topcoat. The coating then often appears dusty, which is undesirable. Another advantage of the described mixtures is that the pH of the inorganic binder and / or the coating composition can be set in the acidic range, without precipitating the silicates or silicic acid.

[0020] Particularly good results are obtained in this connection when the inorganic binder is a silane-modified silicate compound or a silane-modified water glass, which is usually obtainable by at least partial hydrolysis and / or condensation of at least one silane in the presence of at least one silicate at a pH of 8 or higher. Similarly, when a silane-modified silicate compound or a silane-modified water glass is used, no carbonation is observed and the pH of the inorganic binder or coating composition can be set to a value of 7 or less without silicate precipitation. In this case, the pH can be adjusted by adding an acid. The use of the silane-modified silicate compound or the silane-modified water glass in the neutral or acidic pH range is preferred, since the absorption of carbon dioxide, especially in the form of carbonate, is significantly reduced in the acidic range.

[0021] Preferably, the process for producing the silane-modified silicate or silane-modified water glass is carried out in such a way that the silane is at least partially hydrolyzed in the presence of a silicate compound or water glass at a pH of 8 or more, in particular above 11, to give the silane-modified silicate or water glass, and then the pH is set to a value below 8.5, in particular below 8, preferably within the range of 4 to 7, in particular by adding an acid. During acidification, a pH value of 2-4 may also be set and achieved and maintained without precipitation or agglomeration of said silane modified silicate compound or silane modified water glass. Only when partial hydrolysis or condensation of silanes occurs in the presence of silicates in alkaline aqueous solution, beneficial effects are already seen. However, hydrolysis or condensation of silanes in the presence of silicates to form silane-modified silicate compounds or silane-modified water glass is often carried out completely in alkali. Partial hydrolysis of silanes and silicates in alkaline aqueous solution can be continued until complete hydrolysis, if necessary, after acidification to pH 7 or less. Furthermore, according to this embodiment, in particular the aforementioned compounds lithium water glass, sodium water glass, potassium water glass and mixtures thereof, preferably sodium water glass, potassium water glass and mixtures thereof, are used as water glass or silicate. For the preparation of silane-modified silicate compounds or water glass, epoxy-functional, phenoxy-functional, vinyl-functional or amino-functional silanes are advantageously used. More preferably, silanes having at least one Si-C bond, i.e. a bond between silicon and carbon atom, are used. Different silanes may be used in mixture with each other.Particularly preferred silanes are methacryloxymethyltrimethoxysilane, methacryloxymethyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and 3-mercaptopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-cyclohexyl ... Aminopropyltrimethoxysilane, N-cyclohexylamino-methyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-(2-aminomethylamino)propyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-ureidopropyltrimethoxysilane, vinyltrimethoxysilane, vinyldimethoxymethylsilane, vinyltriethoxysilane, vinyltriacetoxysilane, 3-methacryloxy Propyltrimethoxysilane, methacryloxymethyl)methyldimethoxysilane, methacryloxymethyltrimethoxysilane, 3-methacryloxypropyltriacetoxysilane, N-methyl[3-(trimethoxysilyl)propyl]carbamate, N-trimethoxysilylmethyl-O-methylcarbamate, N-dimethoxy(methyl)silylmethyl-O-methylcarbamate, tris-[3-(trimethoxysilyl)propyl]-isocyanurate, 3-glycidoxypropyltrimethoxysilane, Examples of suitable silanes include 3-glycidoxypropyltriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, isooctyltrimethoxysilane, isooctyltriethoxysilane, hexadecyltrimethoxysilane, (cyclohexyl)methyldimethoxysilane, dicyclopentyldimethoxysilane, phenyltriethoxysilane, triacetoxyethylsilane, and 1,2-bis(triethoxysilyl)ethane.

[0022] In the preparation of the silane-modified silicate, the silane and the silicate are advantageously used in a weight ratio of 2:1 to 1:10, in particular 1:1 to 1:5, preferably 1:1 to 1:3, more preferably 1:1 to 1:2. The silane can be used as a single compound or a silane mixture, and the same applies to the silicate. For further details on the preparation of the silane-modified silicate or water glass, reference can be made to WO 2016 / 107791 A1, the disclosure of which is fully incorporated in the present invention. When a mixture of organic and inorganic binders is used in the context of the present invention, particularly good results are obtained when said inorganic and organic binders are used in a specific weight ratio to each other.In the context of the present invention, particularly good results are obtained when the weight ratio of inorganic binder to organic binder varies within the range of 1:1.2 to 3:1, in particular 1:1 to 2:1, preferably 1.1:1 to 1.8:1, more preferably 1.1:1 to 1.4:1, based on the weight of inorganic binder and the weight of organic binder in the coating composition.Thus, in the context of the present invention, it is preferred when a certain excess amount of inorganic binder is used.

[0023] As mentioned above, the coating composition comprises a lubricant, which is preferably selected from the group consisting of organic lubricants, inorganic lubricants and mixtures thereof. However, in the context of the present invention, particularly good results are obtained when the lubricant is an organic lubricant. The lubricants used in the context of the present invention are usually in particulate form, in which respect they typically have absolute particle sizes in the micrometer range. Particularly good results are obtained in the context of the present invention when the lubricant is selected from the group consisting of wax, plastic particles, in particular polyetherketone (PEK), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyethersulfone (PES), polyetherimide (PEI), polyamideimide (PAI) and mixtures thereof, finely divided sulfur and mixtures thereof.Particularly good results are obtained in the context of the present invention when the lubricant is wax. When the lubricant is a wax, it is well documented that the wax is selected from the group consisting of natural waxes, semi-synthetic waxes, synthetic waxes, and mixtures thereof. Preferably, the wax is a synthetic wax.

[0024] Likewise, in the context of the present invention, it is preferred if the wax is selected from the group consisting of beeswax, carnauba wax, montan wax, modified montan wax, amide wax, polypropylene wax, polyethylene wax, HDPE wax (high density polyethylene wax), oxidized HDPE wax, ethylene vinyl acetate wax, polyethylene glycol wax, polyester wax, Fischer-Tropsch wax, and mixtures thereof, preferably polypropylene wax, polyethylene wax, HDPE wax, oxidized HDPE wax, ethylene vinyl acetate wax, polyethylene glycol wax, polyester wax, Fischer-Tropsch wax, and mixtures thereof. In this connection, particularly good results are obtained when the wax is selected from the group consisting of polypropylene waxes, polyethylene waxes, HDPE waxes, oxidized HDPE waxes, Fischer-Tropsch waxes, and mixtures thereof. Even more preferably in the context of the present invention, said wax is a polyethylene wax (PE wax). Waxes, especially synthetic waxes, preferably polyethylene waxes, can be used as lubricants to set particularly good sliding and friction properties of the coating composition. In particular, the combination of organic binders, inorganic binders, wax-based lubricants and platelet-shaped pigments shows a good and consistent coefficient of friction, especially under multiple clamping and thermal stress.

[0025] Here, with regard to the amount in which the coating composition comprises the lubricant, this is at least 1.3 wt.%, based on the coating composition, but it has been found to be advantageous when the coating composition comprises an amount of the lubricant of more than 1.3 wt.%, in particular more than 2 wt.%, preferably more than 3 wt.%, more preferably more than 4 wt.%, in particular more preferably more than 4.5 wt.%, based on the coating composition. Likewise, good results are obtained when the coating composition comprises said lubricant in an amount of less than 20 wt.%, in particular less than 15 wt.%, preferably less than 12 wt.%, more preferably less than 8 wt.%, based on the coating composition. Furthermore, in the context of the invention it is preferred if the coating composition comprises said lubricant in an amount of 1.3 to 20 wt.%, in particular 2 to 15 wt.%, preferably 3 to 12 wt.%, more preferably 4 to 10 wt.%, particularly preferably 4.5 to 8 wt.%, based on the coating composition.

[0026] In the context of the present invention, it is advantageously provided that said coating composition does not contain fluorine-containing compounds, in particular does not contain organic fluorine-containing compounds.Even more preferably, it is provided in the context of the present invention that said coating composition does not contain fluoropolymer particles, in particular does not contain PTFE and PVDF. It is an outstanding advantage of the present invention that it is possible to provide coating compositions with selectively adjustable coefficients of friction without the use of fluoropolymer particles, which is of concern. In particular, in the context of the present invention, it is possible to provide coating compositions that can be used without the use of any fluorinated organic compounds and that have excellent sliding and friction properties. Furthermore, within the scope of the present invention, it is possible to significantly reduce the variability of the coefficient of friction, i.e. the variability of the measured coefficient of friction of a coating composition compared to a coating composition containing fluoropolymer particles.

[0027] Furthermore, within the scope of the present invention, the coating composition comprises platelet-shaped particles. It is well documented that the platelet-shaped particles are selected from the group of metal flakes, graphene, graphite, boron nitride, molybdenum disulfide, glass flakes, layered silicates, and mixtures thereof. The layered silicates are preferably selected from the group of mica, talc, bentonite, kaolin, and mixtures thereof. In this context, the metal flakes are preferably selected from the group of aluminum flakes, zinc flakes, copper flakes, and mixtures thereof. Preferably, the platelet-shaped particles are metal flakes, in particular selected from the group of aluminium flakes, zinc flakes, copper flakes and mixtures thereof, more preferably when the platelet-shaped particles are aluminium flakes. Preferably, the coating composition contains said platelet-shaped particles in an amount of 3 to 15 wt.%, in particular 4 to 12 wt.%, preferably 4 to 10 wt.%, more preferably 5 to 8 wt.%, based on the coating composition. By using platelet-shaped particles in the coating composition, the coefficient of friction and the sliding properties of the coated substrate can be precisely set and, in particular, the stick-slip effect can be much better avoided. Moreover, it is also possible to cure the coating composition at high temperatures without observing an increase in the coefficient of friction.

[0028] Particularly good results are obtained when the weight ratio of the platelet-shaped particles to the lubricant varies within the range of 0.8:1 to 1.8 to 1, in particular 1:1 to 1.6:1, preferably 1.1:1 to 1.4:1, based on the weight of the platelet-shaped particles and the weight of the lubricant in the coating composition. Furthermore, very good results are obtained when there is a specific ratio of platelet-shaped particles to binder.Thus, it has been well documented that the ratio based on weight of platelet-shaped particles to binder is within the range of 1:2 to 1:17, in particular 1:2.4 to 1:9, preferably 1:2.5 to 1:4, more preferably 1:2.7 to 1:3.2, based on the weight of platelet-shaped particles and the weight of binder in the coating composition. In the context of the present invention it may further be provided that said coating composition contains at least one thickener and / or rheological additive. The thickeners and / or rheological additives serve inter alia to set the viscosity and flow or even the layer thickness with which the compositions of the invention can be applied to a substrate. If the coating composition comprises a thickener and / or a rheological additive, the coating composition typically comprises said thickener and / or said rheological additive in an amount of 0.01 to 5 wt.%, in particular 0.05 to 3 wt.%, preferably 0.1 to 2 wt.%, based on the coating composition. The thickener and / or the rheological additive can be selected from a variety of suitable compounds and compound classes. However, it is well documented that the thickener and / or the rheological additive is selected from the group of ethyl cellulose, silicic acid, silicates, and mixtures thereof. More preferably, the thickener and / or the rheological additive is silicic acid, in particular fumed silica.

[0029] According to a further preferred embodiment of the invention, the coating composition comprises (a) a binder; (b) a lubricant, in particular a wax, in an amount of at least 1.3 wt. % based on the coating composition; (c) platelet-shaped particles, in particular metal flakes, and (d) Thickeners and / or rheological additives. For such preferred embodiments of the present invention, all advantages, features and special properties mentioned above in connection with the further embodiments and features of the coating composition of the present invention apply accordingly.

[0030] In addition, it may be provided that the coating composition contains at least one further additive. If the coating composition contains further additives, the coating composition contains said further additives in an amount of 0.01 to 5 wt.%, in particular 0.05 to 3 wt.%, preferably 0.1 to 2 wt.%, based on the coating composition. In this connection, particularly good results are obtained when the further additives are selected from the group consisting of wetting agents, preservatives, stabilizers, acids and / or bases, antifoam compounds, film formers, leveling agents, UV absorbers, fillers, pH stabilizers and pH regulators. Thus, according to a preferred embodiment of the present invention, it is provided that the coating composition comprises (a) a binder; (b) a lubricant, in particular a wax, in an amount of at least 1.3 wt. % based on the coating composition; (c) platelet-shaped particles, especially metal flakes; (d) thickening and / or rheological additives, and (e) Further additives. With respect to such specific and preferred embodiments of the invention, all advantages, features and special properties discussed above in connection with further embodiments and features of the invention apply where appropriate.

[0031] It may further be provided that the coating composition contains a filler. When the coating composition contains a filler, the coating composition typically contains the filler in an amount of 1.3 to 50 wt.%, in particular 1 to 40 wt.%, preferably 5 to 35 wt.%, more preferably 10 to 30 wt.%, based on the coating composition. Particularly good results are obtained when the filler is selected from calcium carbonate, barium sulfate, talc, and mixtures thereof. Thus, according to a further embodiment of the present invention, it is provided that the coating composition comprises (a) a binder; (b) a lubricant, in particular a wax, in an amount of at least 1.3 wt. % based on the coating composition; (c) platelet-shaped particles, especially metal flakes; (d) thickening and / or rheological additives; (e) further additives, and (f) Filler. For such specific embodiments of the invention, all advantages, features and special characteristics discussed above in relation to other embodiments and features of the invention apply, where applicable.

[0032] As mentioned above, in the context of the present invention, the best results are obtained when the coating composition contains an organic binder and an inorganic binder. Thus, in the context of the present invention, particularly good results are obtained when the coating composition contains (a1) an organic binder; (a2) Inorganic binder (b) a lubricant in an amount of at least 1.3 wt. % based on the coating composition; and (c) Platelet-shaped particles. The coating composition may contain almost any amount of the organic binder, but it is well documented when the coating composition contains the organic binder in an amount of 2 to 20 wt.%, in particular 3 to 15 wt.%, preferably 4 to 12 wt.%, more preferably 5 to 10 wt.%, based on the coating composition. Furthermore, it is well documented if the coating composition comprises the inorganic binder in an amount of 4 to 20 wt.%, in particular 6 to 18 wt.%, preferably 7 to 15 wt.%, more preferably 8 to 13 wt.%, based on the coating composition. The use of inorganic binders improves the wear resistance and mechanical properties of coatings in particular.In addition, the use of inorganic coatings is commercially desirable, since inorganic coatings are often inexpensive to prepare or obtain on a large industrial scale.When the coating composition comprises inorganic binders, the inorganic binders are typically silicon-containing binders.

[0033] Furthermore, it is well documented if the weight ratio of the platelet-shaped particles to the organic binder is in the range of 1:0.8 to 1:5, in particular 1:1 to 1:3, preferably 1:1 to 1:2, more preferably 1:1.1 to 1:1.4, based on the weight of the platelet-shaped particles and the weight of the organic binder in the coating composition. Similarly, it is well documented if the weight ratio of the platelet-shaped particles to the inorganic binder is in the range of 1:1.2 to 1:12, in particular 1:1.4 to 1:6, preferably 1:1.5 to 1:2, more preferably 1:1.6 to 1:1.8, based on the weight of the platelet-shaped particles and the weight of the inorganic binder in the coating composition. For such preferred embodiments of the present invention, all advantages, features and special properties mentioned above in connection with the further embodiments and features of the coating composition of the present invention apply accordingly.

[0034] According to a further preferred embodiment of the invention, the coating composition comprises (a1) an organic binder, in particular, the organic binder comprises a polymer selected from the group consisting of acrylates and acrylate copolymers; (a2) inorganic binders, in particular silicon-containing binders; (b) a lubricant, in particular a wax, in an amount of at least 1.3 wt. % based on the coating composition; (c) platelet-shaped particles, in particular metal flakes, and (d) Thickeners and / or rheological additives. For such preferred embodiments of the present invention, all advantages, features and special properties mentioned above in connection with the further embodiments and features of the coating composition of the present invention apply accordingly. According to a further preferred embodiment of the invention, the coating composition comprises (a1) an organic binder, in particular, the organic binder comprises a polymer selected from the group consisting of acrylates and acrylate copolymers; (a2) inorganic binders, in particular silicon-containing binders; (b) a lubricant, in particular a wax, in an amount of at least 1.3 wt. % based on the coating composition; (c) platelet-shaped particles, in particular metal flakes, and (d) thickening and / or rheological additives, and (e) Further additives. For such preferred embodiments of the present invention, all advantages, features and special properties mentioned above in connection with the further embodiments and features of the coating composition of the present invention apply accordingly. According to a further preferred embodiment of the invention, the coating composition comprises (a1) an organic binder, in particular, the organic binder comprises a polymer selected from the group consisting of acrylates and acrylate copolymers; (a2) inorganic binders, in particular silicon-containing binders; (b) a lubricant, in particular a wax, in an amount of at least 1.3 wt. % based on the coating composition; (c) platelet-shaped particles, in particular metal flakes, and (d) thickening and / or rheological additives, and (e) further additives, and (f) Filler. For such particular embodiments of the invention, all advantages, features and special properties mentioned above in relation to the further embodiments and features of the invention apply accordingly.

[0035] As mentioned above, the composition of the present invention is a water-based composition, i.e., the composition of the present invention contains water as a solvent or dispersant. Typically, the composition of the present invention contains water in an amount of 40 to 98 wt.%, particularly 50 to 95 wt.%, preferably 60 to 90 wt.%, more preferably 60 to 85 wt.%, based on the coating composition. In addition, the coating composition preferably contains only small amounts of organic solvents and volatile organic compounds (VOCs).Typically, the coating composition contains organic solvents and volatile organic compounds in an amount of less than 3 wt.%, particularly less than 1 wt.%, preferably less than 0.5 wt.%, more preferably less than 0.3 wt.%, particularly preferably less than 0.1 wt.%, based on the coating composition.Preferably, the coating composition does not contain organic solvents and volatile organic compounds. Now, as far as the viscosity of the coating composition of the invention is concerned, this may vary in a wide range. However, in the context of the present invention, particularly good results are obtained if the coating composition has a Brookfield dynamic viscosity at 20° C. in the range of 2 to 5,000 mPas, in particular 5 to 1,000 mPas, preferably 5 to 500 mPas, more preferably 10 to 100 mPas, particularly preferably 30 to 50 mPas. With a viscosity in the abovementioned range, a particularly thin and uniform topcoat coating can be obtained.

[0036] A further subject of the present invention is - according to a second aspect of the invention - the use of a coating composition as described above as a topcoat for producing a coating having a selectively adjustable coefficient of friction on a metal substrate, in particular a metal substrate provided with a cathodic corrosion protection coating. For further details on this aspect of the invention, reference can be made to the descriptions in the other aspects of the invention, which are applicable according to the uses of the invention.

[0037] A further subject of the invention is also - according to a third aspect of the invention - a method for producing a coating having a selectively adjustable coefficient of friction, (a) in a first method step, providing a substrate having a cathodic corrosion prevention coating on at least a portion of the substrate; (b) in a second method step subsequent to the first method step (a), a coating composition according to any one of claims 1 to 14 is applied to at least a partial area of ​​the substrate, and (c) In a third method step subsequent to said second method step (b), the coating composition applied in said second method step (b) is dried. In the context of the present invention it is particularly preferred if the coating composition applied to the substrate in the second method step (b) is cured and / or crosslinked in the third method step (c). Typically, the substrate contains or consists of a metal. Preferably, the substrate consists of a metal. In this connection, particularly good results are obtained when the metal is selected from the group consisting of iron, aluminum, magnesium, and mixtures and alloys thereof. In the context of the present invention, it is preferred if said metal is selected from iron and its alloys, in particular steel. In the context of the present invention, substrate means an article which can be coated with said coating composition. Typically, in the context of the present invention, said substrate is selected from sheets, moulded articles, small parts and mixtures thereof. In this connection it is preferred if the substrate is a small part, preferably a mass bulk material, in particular selected from screws, nuts, bolts, washers, rivets and mixtures thereof. In the context of the present invention it is preferred if said substrate is a screw or a nut, in particular a bolt.

[0038] A particular advantage of the coating composition of the invention and the method of the invention, namely the specific setting of the coefficient of friction, is particularly effective in the case of threads. With regard to the cathodic corrosion prevention coating, insofar as it is applied to the substrate at least in some areas, preferably over the entire surface, it usually contains a metal selected from the group consisting of zinc, aluminum, magnesium, nickel, and mixtures and alloys thereof. Preferably, the cathodic corrosion protection coating contains zinc and its alloys. In the context of the present invention, it is well documented if the cathodic corrosion protection coating is selected from the group of zinc-containing coatings, in particular electroplated zinc coatings, in particular electroplated zinc-nickel coatings, hot-dip galvanized coatings, zinc powder coatings, in particular zinc paints, and zinc flake coatings. Preferably, the cathodic corrosion protection coating is selected from the group of electroplated zinc coatings, in particular electroplated zinc-nickel coatings, zinc powder coatings, and zinc flake coatings. Zinc powder coatings and zinc flake coatings may in particular also contain zinc alloys. Preferably, the zinc alloy contains, in addition to zinc, aluminum and / or magnesium, preferably aluminum and magnesium. In the context of the present invention, it has been well documented if, in method step (b), the coating composition is applied to a substrate or a cathodic corrosion protection coating in a layer thickness in the range of 1 to 12 μm, in particular 1 to 10 μm, preferably 1 to 8 μm, more preferably 2 to 8 μm and very preferably 2 to 7 μm.

[0039] The coating composition may be applied in process step (b) by any suitable method. However, typically, in method step (b) the coating composition is applied to the substrate by spraying, brushing, scraping, rolling, dipping or dip spinning. Particularly good results are obtained when the coating composition is applied in method step (b) by dipping or dip spinning. Dipping or dip spinning is particularly suitable for coating large amounts of bulk material, such as small parts. Within the scope of the present invention, it is preferred if the coating composition is applied to the entire surface of the substrate or the cathodic corrosion protection coating. The temperature at which said coating composition is dried in process step (c) can vary over a wide range depending on the substrate selected, the cathodic corrosion prevention coating applied thereto, and the coating composition applied. However, it has proven useful if, in method step (c), the coating composition is dried at a temperature in the range of from 20 to 300°C, in particular from 30 to 250°C, preferably from 40 to 200°C, more preferably from 50 to 180°C, even more preferably from 55 to 160°C and most preferably from 60 to 150°C. The above temperatures usually result in rapid drying or curing and / or crosslinking of the binder system while avoiding decomposition of the organic binder. Likewise, it has been found to be advantageous, in process step (c), if the coating composition is dried for a period of from 1 to 30 minutes, in particular from 2 to 25 minutes, preferably from 3 to 20 minutes, more preferably from 5 to 15 minutes.

[0040] As mentioned above, within the scope of the present invention, it is possible to set the coefficient of friction of the resulting coating, in particular the topcoat, in a targeted manner. Thus, particularly good results are obtained when the coefficient of friction of the coated substrate, determined according to DIN EN ISO 16047:2013-01, is set within the range of 0.09 to 0.16 by applying the coating composition. In particular, the coefficient of friction is set by matching the individual components of the coating composition, in particular the amount of organic and inorganic binders, the type and amount of lubricant, and the amount of platelet-shaped particles. For further details on this aspect of the invention, reference can be made to the above descriptions of the other aspects of the invention, which apply appropriately in relation to the use of the present invention.

[0041] Finally, a further subject of the present invention is - according to a fourth aspect of the invention - a metal substrate having a coating obtainable in particular by means of a coating composition as described above or according to a method as described above, said coating containing a lubricant in an amount of at least 4.5 wt.%, based on said coating. It has proven advantageous when the coating comprises an amount of said lubricant of more than 4.5 wt.%, in particular more than 5 wt.%, preferably more than 10 wt.%, more preferably more than 12 wt.% and particularly preferably more than 15 wt.%, based on the coating. Likewise, good results are obtained when the coating has an amount of said lubricant of less than 35 wt.%, in particular less than 30 wt.%, preferably less than 25 wt.%, more preferably less than 22 wt.%, particularly preferably less than 20 wt.%, based on the coating. Furthermore, in the context of the present invention it is preferred if the coating comprises said lubricant in an amount of 4.5 to 35 wt.%, in particular 5 to 30 wt.%, preferably 10 to 25 wt.%, more preferably 12 to 22 wt.%, particularly preferably 15 to 20 wt.%, based on the coating. Usually, the substrate still contains the cathodic corrosion protection coating in the coating, especially the topcoat, especially in the form of a basecoat. In this case, the coating, in particular the topcoat, preferably has a layer thickness in the range from 1 to 10 μm, in particular from 1 to 8 μm, preferably from 1 to 7 μm, more preferably from 2 to 7 μm and particularly preferably from 2 to 6 μm.

[0042] Typically, the coating, in particular the topcoat, has the binder in an amount of 30 to 90 wt.%, in particular 39 to 90 wt.%, preferably 45 to 80 wt.%, more preferably 50 to 70 wt.%, particularly preferably 55 to 65 wt.%, based on the coating, in particular the topcoat. When using mixtures of organic and inorganic binders within the scope of the present invention, it has been well documented that the coating, in particular the topcoat, comprises the organic binder in an amount of 5 to 35 wt.%, in particular 9 to 35 wt.%, preferably 15 to 32 wt.%, more preferably 20 to 30 wt.%, particularly preferably 25 to 30 wt.%, based on the coating, in particular the topcoat. Likewise, in the context of the present invention, it is preferred if the coating, in particular the topcoat, comprises the inorganic binder in an amount of 25 to 75 wt.%, in particular 30 to 60 wt.%, preferably 30 to 50 wt.%, more preferably 30 to 40 wt.%, particularly preferably 32 to 35 wt.%, based on the coating, in particular the topcoat. It is further well documented if the weight ratio of inorganic binder to organic binder is in the range of 1:1 to 2.25:1, in particular 1.1:1 to 2.0:1, preferably 1.2:1 to 1.5:1, based on the weight of inorganic binder and the weight of organic binder in the coating, in particular the topcoat. It is also preferred if the coating, in particular the topcoat, comprises said platelet-shaped particles in an amount of 1 to 30, in particular 10 to 30 wt.%, preferably 15 to 25 wt.%, more preferably 17 to 22 wt.%, based on the coating.

[0043] Particularly good results are obtained when the weight ratio of platelet-shaped particles to lubricant is in the range of 0.8:1 to 1.8:1, in particular 1:1 to 1.6:1, preferably 1.1:1 to 1.4:1, based on the weight of platelet-shaped particles and the weight of lubricant in the coating, in particular the topcoat. Furthermore, very good results can be obtained when a special ratio of platelet-shaped particles to binder is indicated. Thus, it has been well documented when the weight ratio of platelet-shaped particles to binder is within the range of 1:2 to 1:17, in particular 1:2.4 to 1:9, preferably 1:2.5 to 1:4, more preferably 1:2.7 to 1:3.2, based on the weight of platelet-shaped particles and the weight of binder in the coating, in particular the topcoat. When the coating comprises a mixture of organic and inorganic binders, it is well documented that the weight ratio of platelet-shaped particles to organic binder is in the range of 1:0.8 to 1:5, in particular 1:1 to 1:3, preferably 1:1 to 1:2, more preferably 1:1.1 to 1:1.4, based on the weight of platelet-shaped particles and the weight of organic binder in the coating, in particular the topcoat. Similarly, it is well documented if the weight ratio of platelet-shaped particles to inorganic binder is in the range of 1:1.2 to 1:12, in particular 1:1.4 to 1:6, preferably 1:1.5 to 1:2, more preferably 1:1.6 to 1:1.8, based on the weight of platelet-shaped particles and the weight of inorganic binder in the coating, in particular the topcoat. Furthermore, it is preferred if the coefficient of friction of the coated substrate, determined in accordance with DIN EN ISO 16047:2013-01, varies within the range of 0.09 to 0.16. For further details on the substrate of the present invention, reference can be made to the above-mentioned descriptions in other aspects of the present invention, which are appropriately applied to the substrate of the present invention. The subject matter of the present invention is specified below in an illustrative and non-limiting manner with reference to examples. EXAMPLES

[0044] To further illustrate the invention and its advantages, a series of tests are carried out with the topcoat composition of the invention. For this purpose, the coating composition is first applied to a thread and cured. The sliding and frictional properties of the thread are then determined. The results are then compared with the frictional properties of a thread coated with a prior art topcoat composition containing PTFE.

[0045] 1. Topcoat of the present invention The coating composition 1 of the invention for producing the top coat 1 contains a pure acrylate as an organic binder and a mixture of a silane hydrolysate and lithium water glass as an inorganic binder. The coating composition 1 further contains micronized PE wax as a lubricant and aluminum flakes as platelet-shaped particles and further additives. The compositions are shown in Table 1 below. [Table 1]

[0046] 2. Comparative Example of the Topcoat of the Present Invention and a Topcoat Containing PTFE In each case five M 10x65 screws designed as internal supports are first coated with a zinc flake base coat (product DELTA-PROTEKT KL 120 from the company Dorken) which has no lubricating and sliding properties, to a layer thickness of 10 μm. The topcoat of the invention or a topcoat containing PTFE is then applied to the threads coated in this way and cured. The layer thickness in each case is about 3 μm. The product DELTA-PROTEKT VH 301.1 GZ from Dorken contains a mixture of inorganic and organic binders and PTFE as a lubricant and is used as a PTFE-containing topcoat. The coefficient of friction is then determined according to DIN EN ISO 16047:2013-01 with steel as the mating surface. The bolt is tightened and loosened five times each. Head (μhead ) and thread (μ thread ) and then the total coefficient of friction (μ total ) to determine The individual measured values ​​are shown in Table 2 for the topcoat of the present invention and in Table 3 for the comparative example. [Table 2] [Table 3]

[0047] In Figures 1 and 2, the range of measurements, the 25% percentile of the median, and the 75% percentile are plotted for the measurements shown in Tables 2 and 3. b represents the measured coefficient of friction at the head of the screw, and μ th is the measured coefficient of friction in the thread, and μ tot represents the coefficient of total friction. The topcoat of the present invention (FIG. 1) and the PTFE-containing product of the prior art (FIG. 2) both have coefficients of friction determined on both the head and thread, as well as the total coefficient of friction, which are within the required coefficient of friction range of 0.09 to 0.16, with the topcoat of the present invention showing significantly less variability in the individually measured values ​​than the prior art product.

[0048] 3. Effect of baking temperature In a further series of tests, five M 10x65 bolts designed as inner beams are coated with a zinc flake base coat (Dorken product DELTA-PROTEKT KL 100). After curing, the layer thickness is approximately 10 μm. The screws thus coated are then coated with coating composition 1 according to table 1. The coating weight after curing is 2.5-5 g / m2. The curing temperature varies from 60 to 200°C and the curing time is in each case 20 minutes. The coefficient of friction is then determined according to DIN EN ISO 16047:2013-01 with steel as counter layer. The measurement data of the coefficient of friction are shown in table 4. [Table 4] G: Layer weight, g / m 2 T: baking temperature, ℃ As expected, it can be seen that the coefficient of friction remains approximately constant and does not increase with increasing bake temperature.

Claims

1. 1. An aqueous coating composition for producing a coating, in particular a topcoat, having an adjustable coefficient of friction, characterized in that said composition comprises: (a) organic and / or inorganic binders; (b) a lubricant in an amount of at least 1.3 wt. % based on the coating composition; and (c) Platelet-shaped particles.

2. 2. The coating composition according to claim 1, characterized in that the coating composition comprises the binder in an amount of 6 to 40 wt. %, in particular 9 to 33 wt. %, preferably 11 to 27 wt. %, more preferably 13 to 22 wt. %, based on the coating composition.

3. The coating composition of claim 1 , wherein the coating composition comprises an organic and an inorganic binder.

4. 2. The coating composition according to claim 1, characterized in that the organic binder contains or consists of an organic polymer, in particular the organic polymer is selected from the group of acrylates, polyurethanes, polyvinyl acetates, and mixtures and copolymers thereof.

5. The polymer is a mixture of acrylic acid and C 1 - C 10 - Esters with alcohol, methacrylic acid, methacrylic acid and C 1 - C 10 - esters with alcohols, fumaric acid, maleic acid and their mixtures and copolymers, in particular acrylic acid, acrylic acid and C 1 - C 10 - esters with alcohols, methacrylic acid, and methacrylic acid with C 1 - C 10 5. Coating composition according to claim 4, characterized in that it is obtainable from a monomer selected from the group of its esters with hydroxyl-, hydroxyl-, and hydroxyl-alcohols, and their mixtures and copolymers.

6. 10. The coating composition of claim 1, wherein the inorganic binder is selected from silanes, silane hydrolysates, silicates, polysiliconates, and mixtures thereof.

7. 2. The coating composition of claim 1, wherein the lubricant is selected from the group of organic lubricants, inorganic lubricants, and mixtures thereof, preferably organic lubricants.

8. 2. Coating composition according to claim 1, characterized in that the lubricant is selected from the group consisting of waxes, plastic particles, in particular polyetherketone (PEK), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyethersulfone (PES), polyetherimide (PEI), polyamideimide (PAI), and mixtures thereof, micronized sulfur, and mixtures thereof, preferably waxes.

9. 2. The coating composition according to claim 1, characterized in that the coating composition comprises the lubricant in an amount of 1.3 to 20 wt. %, in particular 2 to 15 wt. %, preferably 3 to 12 wt. %, more preferably 4 to 10 wt. %, more preferably 4.5 to 8 wt. %, based on the coating composition.

10. 10. The coating composition of claim 1, wherein the platelet-shaped particles are selected from the group consisting of metal flakes, graphene, graphite, boron nitride, molybdenum disulfide, glass flakes, layered silicates, and mixtures thereof.

11. 2. The coating composition according to claim 1, characterized in that the coating composition contains the platelet-shaped particles in an amount of 3 to 15 wt. %, in particular 4 to 12 wt. %, preferably 4 to 10 wt. %, more preferably 5 to 8 wt. %, based on the coating composition.

12. 2. The coating composition according to claim 1, characterized in that the coating composition is free of fluorine-containing compounds, in particular free of organic fluorine-containing compounds.

13. 13. Use of a coating composition according to any one of claims 1 to 12 as a topcoat for producing a coating with an adjustable coefficient of friction on a metal substrate, in particular a metal substrate provided with a cathodic corrosion protection coating.

14. 1. A method for producing a coating having a selectively adjustable coefficient of friction, comprising: (a) in a first method step, providing a substrate having a cathodic corrosion prevention coating on at least a portion of the substrate; (b) in a second method step subsequent to the first method step (a), applying the coating composition of claim 1 to at least a portion of the substrate; and (c) in a third method step subsequent to said second method step (b), drying the coating composition applied in said second method step (b).

15. 15. The method according to claim 14, characterized in that the coefficient of friction of the coated substrate is set in the range of 0.09 to 0.16, determined in accordance with DIN EN ISO 16047:2013-01.

16. A metal substrate, in particular a metal substrate having a coating obtainable with a coating composition according to any one of claims 1 to 12 or according to the method according to claim 14 or 15, wherein the coating contains a lubricant in an amount of at least 4.5 wt. %, based on the coating.

17. 17. The metal substrate according to claim 16, characterized in that the coating contains the lubricant in an amount of 4.5 to 35 wt. %, in particular 5 to 30 wt. %, preferably 10 to 25 wt. %, more preferably 12 to 22 wt. %, particularly preferably 15 to 20 wt. %, based on the coating.

18. 17. The metal substrate according to claim 16, characterized in that the coating comprises the platelet-shaped particles in an amount of 1 to 30 wt. %, in particular 10 to 30 wt. %, preferably 15 to 25 wt. %, more preferably 17 to 22 wt. %, based on the coating.

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