WO2021043985A1

WO2021043985A1 - Organic-solvent based coating composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate

Info

Publication number: WO2021043985A1
Application number: PCT/EP2020/074773
Authority: WO
Inventors: Lars PLATE
Original assignee: Atotech Deutschland Gmbh
Priority date: 2019-09-04
Filing date: 2020-09-04
Publication date: 2021-03-11
Also published as: TW202116931A; CN114514291A; JP2022546769A

Abstract

The present disclosure is directed to an organic-solvent based coating composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate, the composition comprising (i) at least one organic solvent; (ii) at least one particulate metal provided as metal flakes and having a diameter ranging from 1 pm to 100 µm; (iii) at least one metal carbide at a total concentration ranging from 0.1 wt.-% to 5 wt.-% based on the total weight of the coating composition; and (iv) at least one binding agent.

Description

Organic-solvent based coating composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate

Field of the Invention

The present invention relates to an organic-solvent based coating composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate; and a method for preparing such a composition. The present invention is further directed to a method for coating a surface of a metal substrate; and a metal substrate with a surface comprising such coating.

Background of the Invention

Surfaces of metallic substrates, in particular ferrous metallic substrates, are subject to corrosion, thereby reducing material properties of such corroded metallic surfaces.

Typically, anti-corrosive coatings are applied to the surfaces of metallic substrates to protect the metallic surfaces from corrosion.

Such typical anti-corrosive coatings may comprise chromium coatings. Such chromium coat ings provide an additional barrier layer at the metallic surface, since such chromium coatings are quickly passivated due to contact with ambient air. However, the resulting products of such passivated chromium coatings may impair the decorative and/or functional properties of the surface of the metal substrate.

Alternative anti-corrosive coatings may comprise aqueous and solvent-based anti-corrosion compositions including particulate metals, such as zinc and/or aluminum. Such zinc and/or aluminum coatings are typically electrochemically less noble than the surface of the metal substrate to be coated, thereby providing a cathodic protection of the surface of the metal substrate. Such zinc and/or aluminum coatings can be applied directly to the surface of the metal substrate to provide corrosion protection. However, due to chemical reactions of such less noble zinc and/or aluminum coatings, the resulting products of such coatings may also impair the decorative and/or functional properties of the surface of the metal substrate.

However, the surfaces of many metal substrates typically used in electronics and/or me chanical engineering are subject to mechanical stress during manufacturing, i.e. manufac turing tools can exert mechanical forces on such surfaces.

Besides the anti-corrosive properties, the surfaces of many metal substrates such as metal screws, metal nuts, metal clamps and/or metal springs have to withstand such mechanical forces. Consequently, such metallic surfaces typically comprise an increased coefficient of friction, so that manufacturing tools effectively can exert mechanical forces on the metallic surfaces without slipping off said surfaces.

In GB 1 380 748 a zinc-filled coating composition to be applied to a metal surface is dis closed, wherein the composition comprises silanes and titanium compounds as binding agents.

In GB 1 499 556 a method of hydrolyzing ethyl silicate is disclosed to provide a gellable hydrolysate.

In US 4,209,555 a coating for ferrous metals as cathodic protection is disclosed, wherein the coating is composed of water, zinc dust, aluminum powder, sodium aluminum silicate, iron oxide, titanium dioxide ore, and a thixotrope, such as clay.

In GB 1 212 424 protective coatings containing cross-linked polymeric compositions for ca thodic protection of metal surfaces are disclosed. These cross-linked polymeric composi tions are formed by reaction of a tetra-alkyl titanate ester and polymers resulting from the partial hydrolysis of tetraethyl orthosilicate in an aqueous acidic medium.

In EP 0808883 A2 a water-reducible, chromium-free coating composition for providing cor rosion protection to a metal substrate is disclosed. The coating composition comprises a high-boiling organic liquid, a particulate metal, such as particulate zinc or aluminum, a thick ener, such as hydroxyethylcellulose, and a silane-based binding agent.

In EP 1 280863 A1 a chromium-free coating composition is disclosed, comprising aluminum particles and zinc particles as corrosion inhibitor, and a binder such as silicate and an or ganic titanate.

In US 2007/0259172 coating compositions for providing corrosion protection of metal sub strates are disclosed, wherein the compositions comprise metal particles and a film-forming binder, the binder comprising a titanate and a polyfunctional polymer.

In EP 1 644 451 B1 a chromium-free anti-corrosion coating for metal parts is disclosed, wherein the composition comprises a particulate metal and at least one element selected from yttrium, zirconium, lanthanum, cerium, praseodymium and neodymium as a reinforcing agent for the anticorrosion properties of the composition.

Objective of the present Invention

In view of the prior art, it was thus an object of the present invention to provide an organic-solvent based coating composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate, which shall not exhibit the aforementioned shortcomings of the known prior art coating compositions. In particular, it was an object of the present invention to provide an improved organic- solvent based coating composition which shall be able to provide a coating on a plurality of different kind of metal substrates, in particular ferrous metal substrates.

What is needed therefore is a way to deposit coatings which possess good anti corrosive properties and most preferably in addition good mechanical properties, i.e. an in creased coefficient of friction (correspondingly an increased K-value).

It is another object of the present invention to provide a chromium-free organic-sol- vent based coating composition that approaches or even equals the anti-corrosive and/or mechanical characteristics of chromium coating compositions.

Additionally, it was especially an object of the present invention to provide organic- solvent based coatings, which possess an effective anti-corrosive protection to avoid unde sired corrosion of the coated metal surfaces and which possess an increased coefficient of friction (correspondingly an increased K-value).

It is still another object of the present invention to provide an organic-solvent based coating composition that provides good stability over the life of the composition.

Further, it was an object of the present invention to provide an organic-solvent based coating composition, which shall be also suitable to be used for coating surfaces of metal substrates.

Further, it was an object of the present invention to provide an organic-solvent based coating composition comprising a simple as possible general coating composition, prefera bly with chemicals as cheap as possible.

Summary of the Invention

These objects and also further objects which are not stated explicitly but are imme diately derivable or discernible from the connections discussed herein by way of introduction are achieved by an organic-solvent based coating composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate having all features of claim 1 according to a first aspect of the present invention. Appropriate modifications of the inventive organic-solvent based coating composition are covered in de pendent claims 2 to 12.

Further, claim 13 comprises a method for preparing an organic-solvent based coating composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate according to a second aspect of the present invention. According to a third aspect of the present invention, claim 14 comprises a method for coating a surface of a metal substrate.

According to a fourth aspect of the present invention, claim 15 comprises a metal substrate with a surface, wherein the surface of the metal substrate comprises a coating obtained by a method of coating according to the third aspect.

The invention is in particular suitable for depositing coatings on a surface of a metal substrate for example in the field of coatings for electronics and/or mechanical engineering equipment, where there is a need for protective coatings, e.g. for corrosion protection and in particular additionally with an increased coefficient of friction/(correspondingly an in creased K-value). Typical metal substrates to be coated by the coating composition accord ing to the present invention comprise metal screws, metal nuts, metal clamps and/or metal springs. The basic material of the metal substrate can comprise known ferrous metals, such as iron, steel, i.e. carbon steel, and also mixtures thereof.

The present invention according to the first aspect of the present invention provides an organic-solvent based coating composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate, the composition comprising

(i) at least one organic solvent;

(ii) at least one particulate metal provided as metal flakes and having a diameter ranging from 1 pm to 100 pm;

(iii) at least one metal carbide at a total concentration ranging from 0.1 wt.-% to 5 wt.-% based on the total weight of the coating composition; and

(iv) at least one binding agent.

It is thus possible in an unforeseeable manner to provide an organic-solvent based coating composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate, which does not exhibit the aforementioned shortcom ings of the known prior art coating compositions.

In particular, the organic-solvent based coating composition according to the present inven tion is suitable for depositing a coating on a surface of a metal substrate for increasing the coefficient of friction (correspondingly K-value) of the surface of the metal substrate and to provide an effective anti-corrosion protection of the surface of the metal substrate.

In particular, the organic-solvent based coating composition is suitable for depositing a coat ing on a plurality of different kind of metal substrates, such as iron or steel. The present invention provides a chromium-free organic-solvent based coating composition that at least approaches the coating characteristics of a chromium-based coating composi tion.

The achieved coatings possess good or even excellent anti-corrosive properties and pos sess good or even excellent mechanical properties such as a high coefficient of friction (cor respondingly a high K-value).

Further, the present invention provides an organic-solvent based coating composition that provides good stability over the life of the composition.

Further, the inventive amended organic-solvent based coating composition comprises a very simple general composition with mostly cheap chemicals.

Detailed Description of the Invention

The present invention according to the first aspect provides an organic-solvent based coat ing composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate, the composition comprising

(i) at least one organic solvent;

(iv) at least one binding agent.

The addition of the at least one metal carbide at a total concentration ranging from 0.1 wt- % to 5 wt.-% along with the other above defined features provides a coating composition which enables depositing a coating on the surface of the metal substrate with advantageous properties, such as a good or even excellent (i.e. desired) coefficient of friction (correspond ingly K-value) of the coated surfaces and a good or even excellent corrosion protection.

In the context of the present invention, the terms “for increasing the coefficient of friction” and “increased coefficient of friction” (or a similar but corresponding wording) denote that the present invention must be suitable in order to achieve this effect. This is preferably the case compared to an identical organic-solvent based coating composition with the difference that (iii) is not present or present below or above, respectively, the concentration ranging from 0.1 wt.-% to 5 wt.-%, and/or (ii) is not at least one particulate metal provided as metal flakes and having a diameter ranging from 1 pm to 100 pm. As shown in the examples below, an increased coefficient of friction (correspondingly K-value) is obtained if (ii) and (iii) are set as defined throughout the present text, preferably as defined as being preferred.

Metal carbides possess a high melting point and are extremely hard and abrasion-resistant, thereby allowing for a coating composition to be applied to the metal surface with advanta geous mechanical properties such as an increased coefficient of friction (correspondingly K- value).

In the context of the present invention, the term “metal carbide” includes metal carbides, semi-metal carbides, and transition-metal carbides. Most preferred metal carbides are tran sition-metal carbides.

Providing the at least one binding agent in the composition, allows to provide a coating of the surface of the metal substrate, which does not flake off the surface of the metal substrate. During the coating process, the at least one binding agent fixes the coating on the metal surface to be coated and the at least one binding agent connects the pigments (i.e. the sum of the at least one particulate metal as well as the at least one metal carbide and optional further filler particles) present in the coating composition, thereby ensuring the formation of a permanent and stable coating.

Preferably, the at least one binding agent is adapted to provide a stable dispersion of the at least one particulate metal and the at least one metal carbide in the at least one organic solvent.

In the present invention, the at least one particulate metal is provided as metal flakes.

Preferably, the at least one metal carbide is selected from the group consisting of transition metal carbides and semi-metal carbides, preferably the at least one metal carbide comprises a metal of subgroups IV (“titan group”) to VII (“manganese group”) of the periodic table of elements, preferably titan carbide, tantalum carbide and/or tungsten carbide, and/or a metal of main group III („boron group") and/or main group IV (“carbon group”) of the periodic table of elements, preferably boron carbide and/or silicon carbide, most preferably the at least one metal carbide is selected as tungsten carbide and/or silicon carbide.

A most preferred carbide in the organic-solvent based coating composition is tungsten car bide. Preferred is an organic-solvent based coating composition of the present invention, wherein the at least one metal carbide is not chemically modified. This means that preferably the surface of the at least one metal carbide is not chemically modified. This furthermore pref erably means that the surface of the at least one metal carbide is not chemically modified by an amine moiety and/or a carboxylic moiety.

Preferred is an organic-solvent based coating composition of the present invention, wherein the at least one metal carbide has a diameter of less than 3 pm, preferably of less than 2.5 pm.

Preferred is an organic-solvent based coating composition of the present invention, wherein more than 50 wt.-% of the at least one metal carbide has a diameter of less than 1 pm, based on the total weight of said metal carbide, preferably of 900 nm or less, more preferably of 800 nm or less, even more preferably of 700 nm or less, yet even more preferably of 600 nm or less, most preferably of 500 nm or less.

More preferred is an organic-solvent based coating composition of the present invention, wherein more than 60 wt.-% of the at least one metal carbide has a diameter of less than 1 pm, based on the total weight of said metal carbide, preferably of 900 nm or less, more preferably of 800 nm or less, even more preferably of 700 nm or less, yet even more prefer ably of 600 nm or less, most preferably of 500 nm or less.

Preferably, the coating composition comprises the at least one metal carbide at a total con centration ranging from 0.25 wt.-% to 3.5 wt.-%, preferably from 0.4 wt.-% to 2.4 wt.-%.

By selecting the preferred types of metal carbides and/or by selecting the preferred concen tration ranges of the at least one metal carbide the coating of the surface of the metal sub strate comprises an excellent coefficient of friction (correspondingly K-value) and corrosion protection.

Preferably, the at least one particulate metal comprises particulate aluminum and/or (pref erably and) particulate zinc, and/or the at least one particulate metal comprises a metal-zinc-alloy, wherein the metal comprises aluminum, magnesium, tin, nickel, cobalt and/or manganese, preferably the at least one particulate metal is selected as particulate aluminum and/or (preferably and) particulate zinc. In particular preferred is a composition of the present invention, wherein the at least one particulate metal comprises at least particulate zinc. More preferably, the at least one par ticulate metal comprises particulate zinc and particulate aluminum (preferably as distinct particulate metals), wherein the organic-solvent based coating composition preferably com prises more particulate zinc than particulate aluminum, based on wt.-% and the total weight of the organic-solvent based coating composition. Particularly zinc is needed in order to achieve an acceptable corrosion resistance.

The at least one particulate metal provided as metal flakes have a diameter ranging from 1 pm to 100 pm, preferably from 5 pm to 30 pm.

Preferred is an organic-solvent based coating composition of the present invention, wherein the at least one particulate metal is not a powder. This means that most preferably particu late zinc and particulate aluminum is not present in the organic-solvent based coating com position as a powder. In this context, “powder” typically refers to a diameter of significantly below 1 pm.

A variety of particulate metals, in particular zinc, in the coating composition results in an increased cathodic protection of the coating composition. In particular combining aluminum and zinc as particulate metal, preferably aluminum flakes and zinc flakes, ensures excellent properties of the coating. Together with the at least one carbide as defined above, an ad vantageously high coefficient of friction (correspondingly K-value) is obtained.

Preferably, the at least one particulate metal comprises particulate zinc at a concentration ranging from 31.5 wt.-% to 49.5 wt.-%, based on the total weight of the coating composition.

Preferably, the at least one particulate metal comprises particulate aluminum at a concen tration ranging from 2.6 wt.-% to 9.8 wt.-%, based on the total weight of the coating compo sition.

Preferably, the at least one particulate metal comprises particulate aluminum and particulate zinc preferably at a total concentration ranging from 20 wt.-% to 50 wt.-% based on the total weight of the coating composition, preferably from 30 wt.-% to 50 wt.-%.

By selecting the preferred concentration ranges of the particulate zinc and/or particulate aluminum in the coating composition the coating of the surface of the metal substrate ob tained ensures an excellent cathodic corrosion protection, while in combination with the metal carbide an excellent coefficient of friction (correspondingly K-value) is provided. Preferably, also the particulate aluminum and the particulate zinc are provided as aluminum flakes and zinc flakes, respectively. Also the aluminum flakes and the zinc flakes preferably have a diameter ranging from 1 pm to 100 pm, more preferably from 5 pm to 30 pm.

Providing aluminum flakes and/or zinc flakes (preferably and, and preferably as described throughout the present text as being preferred) allows for an efficient preparation of the coating composition according to the present invention and excellently contributes to an increased coefficient of friction (correspondingly K-value).

The coating composition comprises at least one organic solvent, preferably selected from the group consisting of alcohols, preferably comprising ethanol, iso-propanol, butanol, bu- tan-1-ol, and/or iso-octanol; alkyl ethers of glycol, preferably comprising 1-methoxy-2-pro- panol; mono-alkyl ethers of ethylene glycol; diethylene glycol; propylene glycol; ketones, preferably comprising methyl ethyl ketone and/or methyl isobutyl ketone; iso-phorone; es ters; ethers, preferably comprising 2-ethoxyethyl acetate and/or 2-ethoxyethanol; aromatic hydrocarbons, preferably comprising benzene, toluene and/or xylene; aromatic solvent blends derived from petroleum, preferably comprising hydrogen-treated heavy naphta oil and/or a mixture of aliphatic and naphtenic hydrocarbons with a content of aromatic com pounds less than 0.5 wt.-%; and mixtures thereof.

Preferably, the coating composition comprises the at least one organic solvent at a total concentration ranging from 3 wt.-% to 25 wt.-% based on the total weight of the coating composition, preferably from 4 wt.-% to 15 wt.-%.

The preferred organic solvents and/or the preferred concentration ranges of the organic sol vents allow for an efficient dispersion of all components of the coating composition of the present invention.

Preferably, the coating composition comprises at least one thickening agent, preferably se lected from the group consisting of ethers of hydroxyethylcellulose, methylcellulose, methylhydroxypropylcellulose, ethyl-hydroxyethylcellulose, methylethylcellulose, xanthan gum, urethane-based thickening agents, organically modified clays, preferably organically modified hectorite and/or organically modified smectite clays; fumed silica, hydrophilic fumed silica, modified urea and mixtures thereof.

However, in some cases an organic-solvent based coating composition is preferred not com prising silica.

Preferably, the coating composition comprises at least one wetting agent, wherein preferably the wetting agent is selected as a non-ionic agent, more preferably as non-ionic alkylphenol polyethoxy adducts and/or alkoxylated polyalkylenes, and/or preferably as an anionic wet ting agent, more preferably as organic phosphate esters, and/or a diester sulfosuccinate, even more preferably as sodium bistridecyl sulfosuccinate, and/or more preferably as a low molecular polymethylalkylsiloxane, most preferably polydimethylsiloxane, and modifications thereof, even more preferably as methylalkylpolysiloxane, polyethersiloxane and/or polyes- tersiloxane.

Preferably, the coating composition comprises the at least one thickening agent and/or (pref erably and) the at least one wetting agent at a total concentration ranging from 0.1 wt.-% to 5 wt.-% based on the total weight of the coating composition, preferably from 0.5 wt.-% to 4.0 wt.-%.

By selecting the thickening agent, preferably at the preferred concentrations, the viscosity of the coating composition can be efficiently adjusted. By selecting the wetting agent, pref erably at the preferred concentrations, the surface of the particulate metal and/or the metal carbide can be efficiently wetted.

Preferably, the at least one binding agent comprises at least one

- silane agent, preferably selected from the group consisting of 3-aminopropyltriethox- ysilane, 3-aminopropyltrimethoxy-silane, N-(3-(trimethoxysilyl)propyl)ethylenediamine, N- (3-(triethoxysilyl)propyl)-ethylenediamine, vinyltrimethoxysilane, vinyltriethoxysilane, (3- glycidyloxypropyl)trimethoxysilane, (3-glycidyloxy-propyl)-triethoxysilane, and mixtures, oli gomers and/or hydrolysates thereof, and/or

- monomers and/or oligomers of silica acid ester, preferably selected from the group con sisting of tetramethylorthosilicate, tetraethylorthosilicate, tetrapropylorthosilicate, tetrabu- tylorthosilicate and mixtures, oligomers and/or hydrolysates thereof.

Preferably, the at least one silane agent has a total concentration ranging from 1 wt.-% to 50 wt.-%, based on the total weight of the coating composition, preferably from 2 wt.-% to 35 wt.-%.

In some cases, preferably the at least one binding agent has a total concentration ranging from 1 wt.-% to 50 wt.-%, based on the total weight of the coating composition, preferably from 2 wt.-% to 35 wt.-%.

Preferably, the at least one binding agent comprises (preferably further comprises) at least one titanate compound, preferably comprising a titanium alkoxide, and/or titanium chelate, and/or titanate oligomer formed by partial hydrolysis of titanate monomer, wherein preferably the titanium alkoxide comprises tetra-n-propyl titanate, tetra-iso-propyl titanate, tetra-n-butyl titanate, tetra-tert-butyl titanate and/or tetra-2-ethyl hexyl titanate, wherein preferably the titanium chelate comprises complexes of titanium with at least one dicarbonyl compound, more preferably titanium di-iso-propoxide-bis-(acetylacetonate), tita nium oxy-acetylacetonate, titanium di-iso-propoxide-bis-(2,2,6,6-tetramethyl-3,5-heptanedi- onate), titanium bis-(ethyl-acetoacetato)-di-iso-propoxide, titanium 2-ethyl-1,3-hexanedio- late, di-i-butoxy-bis ethylacetoacetato titanate, and/or a complex of titanium with at least one (poly)hydroxyl carboxylic acid, even more preferably titanium bis-(ammonium-lactato)-dihy- droxide, and/or a chelate complex of titanium with at least one molecule of citric acid, and/or chelate complexes of titanium with a polycarboxyl ic acid, even more preferably with oxalic acid, and wherein preferably the titanate oligomer comprises poly-propyl titanate and/or poly-butyl ti tanate.

Preferably, the at least one titanate compound has a total concentration from 1 wt.-% to 50 wt.-%, based on the total weight of the coating composition, more preferably from 10 wt.-% to 45 wt.-%.

Preferably, the at least one binding agent is selected as at least one silane agent and at least one titanate compound (i.e. a mixture of both), wherein preferably the total concentra tion of the at least one silane agent and the at least one titanate compound ranges from 1 wt.-% to 50 wt.-%, based on the total weight of the coating composition, preferably from 20 wt.-% to 45 wt.-%.

The silane binding agent and/or (preferably and) the titanate binding agent, preferably at the preferred concentration ranges, allows to provide a coating of the surface of the metal sub strate, which does not flake off the surface of the metal substrate.

Very preferred is an organic-solvent based coating composition according to the present invention, wherein the at least one binding agent comprises at least one titanate binding agent. A titanate binding agent is of great benefit in order to achieve an excellent corrosion resistance.

Preferably, the organic solvent is free of water or the amount of water in the organic solvent is 1 wt.-% or less, preferably 0.1 wt.-% or less. Most preferably, the organic-solvent based coating composition of the present invention is free of water or the amount of water in the organic solvent is 1 wt.-% or less, preferably 0.1 wt.-% or less. By using an organic solvent in the coating composition which is (essentially) free of water, the coating effectiveness of the surface of the metal substrate when using such coating composition can be increased.

Preferred is an organic-solvent based coating composition according to the present inven tion, wherein said composition is substantially free of, preferably does not comprise, a lubri cant. This ensures an increased coefficient of friction (correspondingly K-value). More pre ferred is an organic-solvent based coating composition according to the present invention, wherein said composition is substantially free of, preferably does not comprise, a polypro pylene wax, preferably is substantially free of, preferably does not comprise, a polyalkylene wax, most preferably is substantially free of, preferably does not comprise, any wax. Typi cally, lubricants and waxes decrease the coefficient of friction, which is not desired in the context of the present invention.

According to a second aspect, the present invention is directed to a method for preparing an organic-solvent based coating composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate, the method com prising the steps

(a) providing at least one organic solvent and at least one binding agent;

(b) providing at least one metal carbide at a total concentration ranging from 0.1 wt- % to 5 wt.-%, based on the total weight of the coating composition;

(c) providing at least one particulate metal provided as metal flakes and having a di ameter ranging from 1 pm to 100 pm; wherein the compounds according to steps (a), (b), and/or (preferably and) (c) are provided together and/or (preferably or) separately, and wherein the compounds according to the steps (a), (b) and/or (preferably and) (c) are preferably provided in a varying order;

(d) mixing the compounds provided during the steps (a) to (c) to obtain said organic- solvent based coating composition.

By mixing the compounds of the compound mixture a homogenous organic-solvent based coating composition can be obtained (i.e. with preferably a homogeneous distribution). Typ ically, first the liquid compounds are provided, before the solid compounds are dispersed within the liquid compounds. Depending on the specific properties and/or solubilities of the various compounds, some of the compounds according to steps (a) to (c) may be provided separately. Alternatively, it is also possible to provide some or all of the compounds accord ing to steps (a) to (c) together. Depending on the specific properties and/or solubilities of the various compounds the order in which said compounds are provided may be varied in respect to the specific compounds used.

Preferably, as a first step (a) the at least one organic solvent together with the at least one binding agent and optional additional liquid components, such as liquid additives, is pro vided, wherein as a second step (b) the at least one metal carbide together with optional additional solid additives is provided, wherein as a third step (c) the at least one particulate metal is provided, wherein as a fourth step (d) the compounds provided during steps (a) to (c) are mixed to obtain the organic-solvent based coating composition.

Preferably, the mixture is stirred between steps (a), (b) and/or (c) for a defined period of time wherein preferably the defined period of time is longer as for liquid components as for solid compounds. The period of time preferably ranges from 1 min to 60 min.

By adjusting the stirring time in respect to providing liquid or solid components an efficient dispersion of the provided components can be achieved.

Preferably, after step (d) the organic-solvent based coating composition is filtered, preferably through a sieve.

By filtering the organic-solvent based coating composition after mixing, compound aggrega tions can be retained thereby ensuring a homogenous organic-solvent based coating com position.

The aforementioned regarding the organic-solvent based coating composition according to the present invention (preferably described as being preferred) preferably applies likewise to the method of the present invention for preparing an organic-solvent based coating com position.

If applicable, the following preferred features preferably apply likewise to the organic-solvent based coating composition according to the present invention.

Preferred for the method, the at least one metal carbide is selected from the group of tran sition metal carbides and/or semimetal carbides, wherein more preferably the least one metal carbide comprises metal ions of subgroups IV (“titan group”) to VII (“manganese group”) of the periodic table of elements, even more preferably titan carbide, tantalum car bide and/or tungsten carbide, and/or metal ions of main group 111 („boron group") and/or main group IV (“carbon group”) of the periodic table of elements, even more preferably boron carbide and/or silicon carbide, and wherein most preferably the least one metal carbide is selected as tungsten carbide and/or silicon carbide. Preferred for the method, the coating composition comprises the least one metal carbide at a total concentration ranging from 0.25 wt.-% to 3.5 wt.-%, preferably from 0.4 wt.-% to 2.4 wt.-%.

Preferred for the method, the at least one particulate metal is selected as particulate alumi num and particulate zinc, and/or wherein the at least one particulate metal is selected as a metal-zinc-alloy, wherein the metal comprises aluminum, magnesium, tin, nickel, cobalt and/or manganese, wherein preferably the at least one particulate metal is selected as par ticulate aluminum and particulate zinc.

In the method, the at least one particulate metal is provided as metal flakes and having a diameter ranging from 1 pm to 100 pm, preferably from 5 pm to 30 pm.

Preferred for the method, the at least one particulate metal comprises particulate zinc at a concentration ranging from 31.5 wt.-% to 49.5 wt.-% based on the total weight of the coating composition

Preferred for the method, the at least one particulate metal comprises particulate aluminum at a concentration ranging from 2.6 wt.-% to 9.8 wt.-% based on the total weight of the coating composition.

Preferred for the method, the at least one particulate metal comprises particulate aluminum and particulate zinc preferably at a total concentration ranging from 20 wt.-% to 50 wt.-% based on the total weight of the coating composition, preferably from 30 wt.-% to 50 wt.-%.

Preferred for the method, the particulate aluminum and/or the particulate zinc are provided as aluminum flakes and/or zinc flakes, wherein preferably the aluminum flakes and/or the zinc flakes have a diameter from 1 pm to 100 pm, more preferably from 5 pm to 20 pm.

Preferred for the method, the coating composition comprises at least one organic solvent selected as alcohol, preferably as ethanol, iso-propanol, butanol, butan-1-ol, and/or iso-oc- tanol, as alkyl ether of glycol, preferably 1-methoxy-2-propanol, as mono-alkyl ether of eth ylene glycol, as diethylene glycol, as propylene glycol, as ketone, preferably methyl ethyl ketone and/or methyl isobutyl ketone, as iso-phorone, as ester or ether, preferably 2-ethox- yethyl acetate and/or 2-ethoxyethanol, as aromatic hydrocarbon, preferably benzene, tolu ene and/or xylene, and/or as aromatic solvent blends derived from petroleum, preferably hydrogen-treated heavy naphta oil, and/or a mixture of aliphatic and naphtenic hydrocarbons with a content of aromatic compounds less than 0.5 wt.-%, and mixtures thereof. Preferred for the method, the coating composition comprises the at least one organic solvent at a total concentration ranging from 3 wt.-% to 25 wt.-% based on the total weight of the coating composition, preferably from 4 wt.-% to 15 wt.-%.

Preferred for the method, the coating composition comprises at least one thickening agent, wherein preferably the thickening agent is selected from the group comprising ethers of hy- droxyethylcellulose, methylcellulose, methylhydroxypropylcellulose, ethyl-hydroxyethyl- cellulose, methylethylcellulose, xanthan gum, urethane-based thickening agent, organically modified clays, more preferably organically modified hectorite and/or organically modified smectite clays, fumed silica, hydrophilic fumed silica, modified urea and mixtures thereof.

Preferred for the method, the coating composition comprises at least one wetting agent, wherein preferably the wetting agent is selected as a non-ionic agent, more preferably as non-ionic alkylphenol polyethoxy adducts and/or alkoxylated polyalkylenes, and/or prefera bly as an anionic wetting agent, more preferably as organic phosphate esters, and/or a diester sulfosuccinate, even more preferably as sodium bistridecyl sulfosuccinate, and/or more preferably as a low molecular polymethylalkylsiloxane, most preferably polydime- thylsiloxane, and modifications thereof, even more preferably as methylalkylpolysiloxane, polyethersiloxane and/or polyestersiloxane.

Preferred for the method, the coating composition comprises the at least one thickening agent and/or the at least one wetting agent at a total concentration ranging from 0.1 wt.-% to 5 wt.-% based on the total weight of the coating composition, preferably from 0.5 wt.-% to 4.0 wt.-%.

Preferred for the method, the at least one binding agent is selected as at least one silane agent, preferably selected as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxy- silane, N-(3-(trimethoxysilyl)propyl)ethylenediamine, N-(3-(triethoxysilyl)propyl)-ethylenedi- amine, vinyltrimethoxysilane, vinyltriethoxysilane, (3-glycidyloxypropyl)trimethoxysilane, (3- glycidyloxy-propyl)-triethoxysilane, monomers and/or oligomers of silica acid ester, more preferably tetramethylorthosilicate, tetraethylorthosilicate, tetrapropylorthosilicate, tetrabu- ty I orth os i I i cate , and mixtures, oligomers and/or hydrolysates thereof.

Preferred for the method, the at least one binding agent is selected as at least one silane agent at a total concentration ranging from 1 wt.-% to 50 wt.-% based on the total weight of the coating composition, preferably from 2 wt.-% to 35 wt.-%.

Preferred for the method, the at least one binding agent is selected as at least one titanate compound, which is preferably selected as titanium alkoxide, and/or titanium chelate and/or titanate oligomer formed by partial hydrolysis of titanate monomer, wherein more preferably the titanium alkoxide comprises tetra-n-propyl titanate, tetra-iso-propyl titanate, tetra-n-butyl titanate, tetra-tert-butyl titanate and/or tetra-2-ethylhexyl titanate, wherein more preferably the titanium chelate comprises complexes of titanium with at least one dicarbonyl com pound, even more preferably titanium di-iso-propoxide-bis-(acetylacetonate), titanium oxy- acetylacetonate, titanium di-iso-propoxide-bis-(2,2,6,6-tetramethyl-3,5-heptanedionate), ti tanium bis-(ethyl-acetoacetato)-di-iso-propoxide, titanium 2-ethyl-1,3-hexanediolate, di-i- butoxy-bis ethylacetoacetato titanate, and/or a complex of titanium with at least one (poly)hydroxyl carboxylic acid, even more preferably titanium bis-(ammonium-lactato)-dihy- droxide, and/or a chelate complex of titanium with at least one molecule of citric acid, and/or chelate complexes of titanium with a polycarboxyl ic acid, even more preferably with oxalic acid, and wherein more preferably the titanate oligomer is poly-propyl titanate and/or poly butyl titanate.

Preferred for the method, the at least one binding agent is selected as at least one titanate compound at a total concentration from 1 wt.-% to 50 wt.-% based on the total weight of the coating composition, even more preferably from 10 wt.-% to 45 wt.-%.

Preferred for the method, the at least one binding agent is selected as at least one silane agent and at least one titanate compound, wherein the total concentration of the at least one silane agent and the at least one titanate compound ranges from 1 wt.-% to 50 wt.-% based on the total weight of the coating composition, preferably from 20 wt.-% to 45 wt.-%.

Preferred for the method, the organic solvent is free of water or wherein the amount of water in the organic solvent is less than 1 wt.-%, preferably less than 0.1 wt.-%.

According to a third aspect, the present invention is directed to a method for coating a sur face of a metal substrate, the method comprising the steps

(A) providing said metal substrate,

(B) providing an organic-solvent based coating composition for coating a surface of a metal substrate, the composition comprising

(i) at least one organic solvent;

(iii) at least one metal carbide at a total concentration ranging from 0.1 wt.-% to 5 wt.-%, based on the total weight of the coating composition; and

(iv) at least one binding agent, (C) contacting the metal substrate with said organic-solvent based coating com position such that a coating is deposited on at least one surface of said metal substrate, and

(D) heating the metal substrate and the coating deposited on the at least one surface of said metal substrate to obtain a surface of said metal substrate with an increased coefficient of friction.

The aforementioned regarding the organic-solvent based coating composition (preferably described as being preferred) preferably applies likewise to the method for coating according to the present invention.

Preferred is a method according to the third aspect, wherein the coating has a thickness ranging from 4 to 20 pm, preferably from 6 to 10 pm.

Preferred is a method according to the third aspect, wherein the coating provides a K-value of 0.28 or more, preferably of 0.29 or more, more preferably of 0.30 or more, even more preferably of 0.31 or more, yet even more preferably of 0.32 or more, most preferably of 0.33 or more.

Preferred is a method according to the third aspect, wherein the coating provides a coeffi cient of friction of 0.22 or more, preferably of 0.23 or more, more preferably of 0.24 or more, even more preferably of 0.25 or more, yet even more preferably of 0.26 or more, most pref erably of 0.27 or more.

In some cases a method according to the third aspect is preferred, wherein at least steps (B), (C), and (D) are repeated, preferably at least a second time. This is preferred if after steps (B), (C), and (D) are utilized a first time, a thicker coating is desired. This can be achieved if preferably the method is carried out two times with a substrate that has already a coating as a result from carrying out the method a first time.

Preferred for the method according to the third aspect, before step (B) the metal substrate is pre-treated, preferably by sandblasting the surface of the metal substrate or by phospha- tizing the surface of the metal substrate.

By performing said pre-treatment step, the surface of the metal substrate can be efficiently modified to improve the contact between the surface of the metal substrate and the coating.

Preferred for the method according to the third aspect, after step (C), the metal substrate is rotated to remove an excess of the coating composition from the metal substrate.

Preferred for the method according to the third aspect, during step (D) the metal substrate is heated to a temperature ranging from 150 °C to 350 °C, preferably from 200 °C to 300 °C. Preferred for the method according to the third aspect, during step (C) the organic-solvent based coating composition is sprayed on the surface of the metal substrate during a spray ing process, and/or during step (C) the metal substrate is immersed in the organic-solvent based coating composition during an immersion process.

Preferred for the method according to the third aspect, the metal substrate comprises a metal screw, a metal nut, a metal clamp and/or a metal spring.

Preferred for the method according to the third aspect, the coated surface of the metal sub strate obtained after step (D) comprises a K-value from 0.3 to 0.5. The value measured to evaluate the coefficient of friction of coated surfaces of metal substrates according to the present invention preferably is the K-value (i.e. the K-value is a representation for the coef ficient of friction although both values are not identical), which is determined by the following equation according to item 10.1 of the norm DIN EN ISO 16047, K = T / F x d, wherein T corresponds to the tightening torque („Anziehdrehmoment“), wherein F corresponds to the preload force („Vorspannkraft“), and wherein d corresponds to the nominal thread diameter („Gewindenenndurchmesser“). For further details a reference to the example section of the present application is provided.

Preferred for the method according to the third aspect, the metal of the metal substrate is a ferrous metal, preferably iron or steel.

Preferred is a method according to the third aspect, wherein in step (C) no electrical current is applied.

According to a fourth aspect, the present invention is directed to a metal substrate with a surface, wherein the surface of the metal substrate comprises a coating obtained by a method for coating according to the third aspect.

The aforementioned regarding the method according to a third aspect of the present inven tion (preferably as described as being preferred) preferably applies likewise to the metal substrate of the present invention.

Preferred for the substrate, the metal substrate comprises a metal screw, a metal nut, a metal clamp and/or a metal spring.

Preferred for the substrate, the coated surface of the metal substrate comprises a K-value from 0.3 to 0.5. For further details in respect to the K-value a reference to the example section of the present application is provided.

Preferred for the substrate, the metal of the metal substrate is a ferrous metal, preferably iron or steel. Examples

The following non-limiting examples are provided to illustrate an embodiment of the present invention and to facilitate understanding of the invention but are not intended to limit the scope of the invention, which is defined by the claims appended hereto.

Organic-solvent based coating compositions

In general, there has to be mentioned, that all experiments, comprising the experiments in accordance with the present invention as well as the comparative embodiments outside of the present invention, have been conducted using an organic-solvent based coating com position, which comprises particulate zinc, particulate aluminum, at least one additive, at least one binding agent, which comprises at least one titanate compound and at least one silane agent, and at least one organic solvent. The particulate zinc and particulate aluminum are provided as flakes having a diameter ranging at least from 5 pm to 15 pm. This is in general a very preferred diameter for the particulate metal utilized in the present invention.

In all experiments the at least one additive comprises hydrophilic fumed silica as thickening agent and polymethylalkylsiloxane as wetting agent.

In all experiments the at least one titanate compound is selected as tetra-n-butyl titanate, polybutyl titanate, titanium bis-(ethyl-acetoacetato)-di-iso-propoxide, and tetra-2-ethylhexyl titanate, tetra-n-propyl titanate, tetra-iso-propyl titanate and tetra-tert- butyl titanate.

In all experiments the at least one silane is selected as (3-glycidyloxypropyl)trimethox- ysilane, (3-glycidyloxy-propyl)-triethoxysilane, 3-aminopropyltriethoxysilane or 3-ami- nopropyltrimethoxy-silane

In all experiments the at least one organic solvent is selected as hydrogen-treated heavy naphta oil, isooctanol, butan-1-ol, and a mixture of aliphatic and naphtenic hydrocarbons with a content of aromatic compounds less than 0.5 wt.-%.

In the organic-solvent based coating composition according to the experiments at least one metal carbide is added, preferably tungsten carbide (D50: 200 nm), abbreviated as WC, and/or silicon carbide, abbreviated as SiC.

To prepare said organic-solvent based coating composition all components are added in a defined order into a container and are mixed by using a dissolver during a pre-dispersion step, which allows for crushing of agglomerated components. For the experiments during a first step the at least one organic solvent is added, during a second step the at least one additive is added, and during a third step the solid components including the particulate aluminum, the particulate zinc, the at least one titanate compound and the at least one silane is added.

After adding each component, the reaction mixture is stirred. Afterwards, the mixture is fil tered through a sieve with a defined mesh size to obtain the organic solvent based coating composition. Afterwards composition parameters, in particular viscosity, density, average particle size and/or solid content, of the organic solvent based coating composition are measured.

Coating of surfaces of metal substrates

The organic-solvent based coating compositions allow for coating a surface of a metal sub strate for increasing the coefficient of friction of the surface of the metal substrate. The metal substrates to be coated comprise metal screws, metal nuts, metal clamps and/or metal springs.

In a first coating step the metal substrate, which is typically lubricated, is cleaned, preferably by an alkaline degreasing agent. In a second coating step, the cleaned metal substrate is pre-treated, preferably by sandblasting the surface of the metal substrate.

In a third coating step the pre-treated metal substrate is immersed in the corresponding coating composition according to the specific example to apply the coating composition to the surface of the metal substrate. Preferably, the pre-treated metal substrate is immersed at 10°C to 35°C for 30 sec to 1 min, and afterwards the pre-treated metal substrate is im mersed at 15°C to 28°C for 30 sec to 1 min. Preferably, the pre-treated metal substrate is moved in the corresponding coating compositions during immersion.

In a fourth coating step the metal substrate is rotated to remove an excess of coating com position from the metal substrate, so that only a thin film of coating composition remains on the surface of the metal substrate.

In a fifth coating step the metal substrate comprising the film of coating composition is heated for a predetermined time to a temperature ranging from 300 °C, preferably at 230 °C for 30 min, to remove volatile components from the coating composition and to allow for a chemical reaction of the remaining components of the coating composition to form a coating on the surface of the metal substrate.

Mechanical properties of coated surfaces of metal substrates

To evaluate the mechanical properties of the various coatings applied to the surfaces of the various metal substrates according to the experiments, the coefficient of friction of the coated surfaces of the various metal substrates is determined according to the norm DIN EN ISO 16047. The coefficient of friction (CoF) and the K-value are proportionally related to each other. During the experiments of the present invention, the K-value as well as the CoF are measured and evaluated.

The coefficient of friction (CoF) of coated surfaces of metal substrates according to the pre sent invention is determined as well as the K-value, wherein the K-value is determined by the following equation according to item 10.1 of the norm DIN EN ISO 16047, K = T / F x d, wherein T corresponds to the tightening torque („Anziehdrehmoment“), wherein F corre sponds to the preload force („Vorspannkraft“), and wherein d corresponds to the nominal thread diameter („Gewindenenndurchmesser“). The CoF was also determined based on DIN EN ISO 16047.

To experimentally determine the K-value, the metal substrate, in particular the metal screw and/or metal nut, are arranged in the test stand, wherein the test stand is adapted to apply a torque value to the metal substrate, and wherein the test stand is adapted to measure a variety of experimental values such as various coefficients of friction. For detailed infor mation on how to derive a K-value from the measured various coefficients of friction refer ence is made to the mathematical relationships according to the norm DIN EN ISO 16047.

Experimental data

All concentrations given in Tables 1 and 2 for the different coating compositions are listed in wt.-% based on the total weight of the coating composition, if not stated differently.

The experiments given in Tables 1 and 2 are numbered in consequent order.

Turning now to the Tables, Table 1 shows conducted experiments for organic-solvent based coating compositions in accordance with embodiments of the present invention, and Table 2 shows comparative experiments for organic-solvent based coating compositions.

Table 1 : Experiments for organic-solvent based coating compositions

Table 2: Comparative experiments for organic-solvent based coating compositions

When comparing experiments 1 to 5 to the comparative experiments 6 and 7 it can be de rived that adding a metal carbide, i.e. silicon carbide (see example 1) and/or tungsten car bide (see examples 2 to 5), results in an increased K-value of the coated surface of the metal substrate derived after a coating process using the respective coating composition.

In particular, increasing the content of tungsten carbide from 0.5 wt.-% (see example 2) to 1.5 wt.-% (see example 4) results in a K-value, which is increased from 0.29 (see example 2) to 0.32 (see example 4). The optimal K-value of 0.35 is obtained when using the compo sition according to example 5, wherein the amount of tungsten carbide is 1.70 wt.-%.

Own experiments have shown that the at least one metal carbide at a total concentration ranging from 0.1 wt.-% to 5 wt.-%, based on the total weight of the coating composition, and the at least one particulate metal provided as metal flakes and having a diameter ranging from 1 pm to 100 pm is very important for obtaining the increased K-value (correspondingly CoF). As shown above, the absence of said at least one metal carbide results in a reduced, insufficient K-value (correspondingly CoF). Similar undesired results are obtained if particu late metal flakes are used having a significantly smaller diameter, e.g. significantly below 1 pm, e.g. as a powder.

Claims

1. An organic-solvent based coating composition for coating a surface of a metal sub strate for increasing the coefficient of friction of the surface of the metal substrate, the composition comprising

(i) at least one organic solvent;

(iv) at least one binding agent.

2. The organic-solvent based coating composition according to claim 1, wherein the at least one metal carbide is selected from the group consisting of transition metal car bides and semi-metal carbides, preferably the at least one metal carbide comprises a metal of subgroups IV (“titan group”) to VII (“manganese group”) of the periodic table of elements, preferably titan carbide, tantalum carbide and/or tungsten carbide, and/or a metal of main group III („boron group") and/or main group IV (“carbon group”) of the periodic table of elements, preferably boron carbide and/or silicon carbide, most preferably the at least one metal carbide is selected as tungsten carbide and/or silicon carbide.

3. The organic-solvent based coating composition according to claim 1 or 2, wherein the coating composition comprises the at least one metal carbide at a total concentration ranging from 0.25 wt.-% to 3.5 wt.-%, preferably from 0.4 wt.-% to 2.4 wt.

4. The organic-solvent based coating composition according to one of the preceding claims, wherein the at least one particulate metal comprises particulate aluminum and/or particulate zinc, and/or the at least one particulate metal comprises a metal-zinc-alloy, wherein the metal com prises aluminum, magnesium, tin, nickel, cobalt and/or manganese, preferably the at least one particulate metal is selected as particulate aluminum and/or particulate zinc.

5. The organic-solvent based coating composition according to one of the preceding claims, wherein the at least one particulate metal provided as metal flakes have a diameter ranging from 5 pm to 30 pm.

6. The organic-solvent based coating composition according to one of the preceding claims, wherein the at least one particulate metal comprises particulate zinc at a con centration ranging from 31.5 wt.-% to 49.5 wt.-%, based on the total weight of the coating composition.

7. The organic-solvent based coating composition according to one of the preceding claims, wherein the at least one particulate metal comprises particulate aluminum at a concentration ranging from 2.6 wt.-% to 9.8 wt.-%, based on the total weight of the coating composition.

8. The organic-solvent based coating composition according to one of the preceding claims, wherein the coating composition comprises at least one thickening agent, pref erably selected from the group consisting of ethers of hydroxyethylcellulose, methyl- cellulose, methylhydroxypropylcellulose, ethyl-hydroxyethylcellulose, methylethyl- cellulose, xanthan gum, urethane-based thickening agents, organically modified clays, preferably organically modified hectorite and/or organically modified smectite clays; fumed silica, hydrophilic fumed silica, modified urea and mixtures thereof.

9. The organic-solvent based coating composition according to one of the preceding claims, wherein the at least one binding agent comprises at least one

- silane agent, preferably selected from the group consisting of 3-aminopropyltriethox- ysilane, 3-aminopropyltrimethoxy-silane, N-(3-(trimethoxysilyl)propyl)ethylenedia- mine, N-(3-(triethoxysilyl)propyl)-ethylenediamine, vinyltrimethoxysilane, vinyltriethox- ysilane, (3-glycidyloxypropyl)trimethoxysilane, (3-glycidyloxy-propyl)-triethoxysilane, and mixtures, oligomers and/or hydrolysates thereof, and/or

- monomers and/or oligomers of silica acid ester, preferably selected from the group consisting of tetramethylorthosilicate, tetraethylorthosilicate, tetrapropylorthosilicate, tetrabutylorthosilicate, and mixtures, oligomers and/or hydrolysates thereof.

10. The organic-solvent based coating composition according to claim 9, wherein the at least one silane agent has a total concentration ranging from 1 wt.-% to 50 wt.-%, based on the total weight of the coating composition, preferably from 2 wt.-% to 35 wt.-%.

11. The organic-solvent based coating composition according to one of the preceding claims, wherein the at least one binding agent comprises at least one titanate com pound, preferably comprising a titanium alkoxide, and/or titanium chelate, and/or titan ate oligomer formed by partial hydrolysis of titanate monomer, wherein preferably the titanium alkoxide comprises tetra-n-propyl titanate, tetra-iso- propyl titanate, tetra-n-butyl titanate, tetra-tert-butyl titanate and/or tetra-2-ethylhexyl titanate, wherein preferably the titanium chelate comprises complexes of titanium with at least one dicarbonyl compound, more preferably titanium di-iso-propoxide-bis-(acety- lacetonate), titanium oxy-acetylacetonate, titanium di-iso-propoxide-bis-(2,2,6,6-tetra- methyl-3,5-heptanedionate), titanium bis-(ethyl-acetoacetato)-di-iso-propoxide, tita nium 2-ethyl-1,3-hexanediolate, di-i-butoxy-bis ethyl acetoacetato titanate, and/or a complex of titanium with at least one (poly) hydroxyl carboxylic acid, even more pref erably titanium bis-(ammonium-lactato)-dihydroxide, and/or a chelate complex of tita nium with at least one molecule of citric acid, and/or chelate complexes of titanium with a polycarboxylic acid, even more preferably with oxalic acid, and wherein preferably the titanate oligomer comprises poly-propyl titanate and/or poly butyl titanate.

12. The organic-solvent based coating composition according to claim 11, wherein the at least one titanate compound has a total concentration from 1 wt.-% to 50 wt.-%, based on the total weight of the coating composition, more preferably from 10 wt.-% to 45 wt.-%.

13. A method for preparing an organic-solvent based coating composition for coating a surface of a metal substrate for increasing the coefficient of friction of the surface of the metal substrate, the method comprising the steps

(a) providing at least one organic solvent and at least one binding agent;

(b) providing at least one metal carbide at a total concentration ranging from 0.1 wt- % to 5 wt.-%, based on the total weight of the coating composition (c) providing at least one particulate metal provided as metal flakes and having a diameter ranging from 1 pm to 100 pm; wherein the compounds according to steps (a), (b), and/or (c) are provided together and/or separately, and wherein the compounds according to the steps (a), (b), and/or

(c) are preferably provided in a varying order;

14. A method for coating a surface of a metal substrate, the method comprising the steps

(A) providing said metal substrate,

(i) at least one organic solvent;

(iv) at least one binding agent,

(C) contacting the metal substrate with said organic-solvent based coating compo sition such that a coating is deposited on at least one surface of said metal sub strate, and

(D) heating the metal substrate and the coating deposited on the at least one surface of said metal substrate to obtain a surface of said metal substrate with an in creased coefficient of friction.

15. A metal substrate with a surface, wherein the surface of the metal substrate comprises a coating obtained by a method for coating according to claim 14.