Lubricating coating for fasteners

Abstract

A lubricating coating for threaded fasteners (1), in particular wheel bolts or wheel nuts, is provided, comprising 30 - 50 wt.% of a polymer matrix, 25 - 50 wt.% fillers and / or anti-corrosion pigments, 3 - 15 wt.% coating additives, 3 - 15 wt.% pigments, dyes and / or metallic effect pigments, 1.0 - 10.0 wt.% polyethylene wax, and 0.5 - 5.0 wt.% synthetic paraffins. Furthermore, a threaded fastener (1) with a lubricating coating as well as a method for the production thereof are provided.

Description

[0001] Lubricant for fasteners

[0002] The present invention relates to a sliding lacquer for screw fasteners, in particular wheel bolts or wheel nuts, a use of the sliding lacquer for coating screw fasteners, a screw fastener with a sliding lacquer coating and a method for producing a screw fastener with a sliding lacquer coating.

[0003] Sliding coatings are coatings that provide lubricating properties, for example, through the inclusion of solid lubricants. Sliding coatings for bolted fasteners, such as wheel bolts or wheel nuts, are applied to their surface and serve to provide corrosion protection and ensure consistent friction behavior even after numerous assembly and disassembly cycles. Sufficient mechanical resistance is therefore essential.

[0004] In the case of a wheel bolt, one of the biggest challenges for a bolted fastener, in addition to maintaining consistent friction during and after repeated assembly, it is also desirable that the lubricant allows for controlled loosening of the bolts during and after high thermal and mechanical stresses, such as those occurring during high-speed cornering with sharp braking maneuvers, ensuring that the wheel bolts are neither too loose nor too tight. A standardized test drive is a so-called thermodynamic tightness test, which involves high thermal and mechanical stresses. These properties of known lubricants still require improvement.In particular, at room temperature (statically), a more consistent lubrication performance with a tendency towards better sliding during repeated tightening and loosening is desirable, as is higher friction and thus poorer sliding during and after thermal stress, since the friction of known sliding coatings generally decreases significantly under thermal stress of 150°C and above. For wheel bolts coated with sliding coating, it is particularly desirable that the ratio of the loosening torque at room temperature after thermal stress, especially a thermodynamic tightness test, to the tightening torque before thermal stress is > 60%, and preferably > 70%.

[0005] Another disadvantage of many well-known sliding coatings is that they contain polyfluoroalkyl substances (PFAS). PFAS are a group of mainly synthetically produced substances used in numerous applications. These applications include their use in textiles, (food) packaging, lubricants, coolants, electronics, construction, and many other areas. The substances are used as individual components (either non-polymeric or polymeric) and as constituents of mixtures and (complex) products for consumer, commercial, and industrial purposes.

[0006] A problem with all PFAS and / or their degradation products that fall within the scope of the EU restriction proposal (Annex XV, version 2 of 22 March 2023) is their very high persistence, which far exceeds the criterion for very persistent (vP) according to Annex XIII of the REACH Regulation. PFAS and their degradation products can remain in the environment longer than any other man-made chemicals. Further reasons for concern include their bioaccumulation, mobility, long-range transport potential (LRTP), bioaccumulation in plants, global warming potential, and (eco)toxicological effects. PFAS enter the environment through emissions during manufacturing, use, and waste.If these substances and their degradation products continue to be released into the environment, the concentration in the environment will increase, as mineralization under natural conditions does not occur for the PFAS that fall within the scope of the EU restriction proposal.

[0007] Once PFAS are present in the environment, their removal from surface water, groundwater, soil, and sediment is technically extremely difficult and costly, if not impossible. Environmental monitoring of PFAS shows that they are ubiquitous, even in organisms, drinking water sources, and foodstuffs, as well as in remote and pristine areas, making exposure for present and future generations unavoidable and irreversible. Ideally, the production and release of new PFAS should be avoided as much as possible.

[0008] The object of the invention is therefore to provide a sliding coating for screw fasteners, in particular for wheel mounting, which exhibits good corrosion resistance and maintains the most consistent possible friction behavior during multiple assembly operations and during and after high thermal and mechanical stress. It is also an object that the sliding coating requires as few polyfluorinated alkyl substances as possible.

[0009] This problem is solved by a sliding coating for screw fasteners, in particular wheel fasteners and especially wheel bolts and wheel nuts, according to claim 1, a use according to claim 8, a screw fastener with a sliding coating according to claim 9, a method for manufacturing a screw fastener according to claim 12, and a use of the screw fastener for fastening a wheel according to claim 13. Further features, embodiments, and advantages will become apparent from the dependent claims and the description. One aspect of the invention relates to a sliding coating for screw fasteners, in particular for wheel bolts and wheel nuts, comprising

[0010] 30 - 50 wt% of a polymer matrix,

[0011] 25 - 50 wt.% fillers and / or corrosion protection pigments,

[0012] 3 - 15 wt.% paint additives,

[0013] 3 - 15 wt.% pigments, dyes and / or metallic effect pigments,

[0014] 1.0 - 10.0 wt.% polyethylene wax and

[0015] 0.5 - 5.0 wt.% synthetic paraffins, where the wt.% refers to the total weight of the lubricant.

[0016] As described below, a sliding lacquer according to the invention is understood to be a dried sliding lacquer.

[0017] Another aspect of the invention relates to the use of the inventive sliding lacquer for coating screw fasteners.

[0018] Another aspect of the invention relates to a screw connection with a sliding lacquer coating, wherein the screw connection has a surface, and a layer of the sliding lacquer according to the invention is applied to at least part of the surface.

[0019] Another aspect of the invention relates to a method for producing a screw connection with a coating made from the inventive sliding lacquer, comprising the steps

[0020] Providing a screw fastener with a surface, dispersing a polymer resin as well as fillers and / or corrosion protection pigments, paint additives, as well as pigments, dyes and / or metallic effect pigments in a solvent,

[0021] Addition of a crosslinking agent, polyethylene wax and synthetic paraffin and optionally further additives to the dispersion, mixing to form a sliding lacquer dispersion, optionally application of a zinc-containing layer to at least part of the surface of the screw connection, optionally application of a layer of adhesion promoter, application of at least one layer of the sliding lacquer dispersion to at least part of the surface of the screw connection, drying of the layer and

[0022] Baking of the layer at a temperature of 140 to 250 °C.

[0023] The screw fasteners according to the invention are preferably wheel fasteners or elements for vehicles such as wheel bolts, wheel nuts or central wheel fasteners such as central bolts or central nuts.

[0024] The sliding coating according to the invention exhibits high corrosion resistance and, surprisingly, also constant friction properties, both during and after multiple assembly processes as well as during and after high thermal and mechanical stress such as that represented by a thermo-dynamic tight fit test.

[0025] The inventive sliding varnish also exhibits very good adhesion (DIN EN ISO 2409) and very good media resistance, in particular against gasoline E10, diesel fuel B7, reference engine oil according to TL52185, hydraulic oil TL52146, coolant TL774, brake fluid TL766, tested according to DIN EN ISO 2812-3.

[0026] The behavior of a wheel bolt coated with the inventive sliding lacquer and subjected to temperature and dynamics in an application-oriented thermo-dynamic tightness test is shown below using the example of wheel bolts with dimensions M14 x 1.5 x 27:

[0027] The above results show that a very constant friction behavior could be achieved according to the invention.

[0028] In the sliding coating according to the invention, the polymer matrix is ​​a polymer that serves as a matrix for the other components; that is, the other components, such as fillers, corrosion protection pigments, coating additives, pigments, dyes and / or metallic effect pigments, as well as polyethylene wax and synthetic paraffin, are distributed within the polymer matrix. Polyethylene wax and synthetic paraffin are also collectively referred to as solid lubricants.

[0029] The polymer matrix is ​​preferably a reaction product of a polymer resin (binder) and a crosslinker (hardener). In a preferred embodiment, the polymer resin is selected from the group consisting of polyamide, polyamide-imide, polyurethane, polyester, acrylate, epoxysilane, epoxysiloxane, phenoxy, epoxy, and mixtures thereof, and / or the crosslinker is selected from the group consisting of isocyanate resin, imidazole resin, phenolic resin, amine resin, for example, melamine resin, benzoguanamine resin, urea resin, and mixtures thereof. It is further preferred that the polymer resin is selected from the group consisting of polyamide, polyamide-imide, polyurethane, polyester, acrylate, phenoxy, epoxy, and mixtures thereof, and / or that the crosslinker is selected from the group consisting of isocyanate resin, phenolic resin, amine resin, and mixtures thereof; even more preferably, the crosslinker is a phenolic resin.

[0030] The polymer matrix is ​​most preferably a reaction product of a polymer resin and a crosslinker, wherein the polymer resin is a phenoxy resin, an epoxy resin, or a mixture thereof, and the crosslinker is a phenolic resin, thermally blocked isocyanate, anhydrite, or an amine resin; most preferably, the crosslinker is a phenolic resin. Suitable catalysts can also be added for a controlled and accelerated chemical reaction between the binder and the hardener.

[0031] In another preferred embodiment, the polymer matrix is ​​a reaction product of

[0032] Polyamide and thermally blocked polyisocyanate, melamine, or epoxy resins

[0033] Polyamideimide

[0034] Polyurethane and polyalcohols saturated polyesters and thermally blocked polyisocyanate, melamine or epoxy resins

[0035] Acrylate, including epoxidized, and thermally blocked polyisocyanate or polyamine resins

[0036] Epoxy and / or phenoxy and polyamine, anhydrite, thermally blocked polyisocyanates or phenolic resins and mixtures thereof.

[0037] Polyamide-imide is self-crosslinking and therefore does not necessarily require a reaction partner.

[0038] With the aforementioned preferred components for the polymer resin and / or the crosslinker, the inventive sliding coating exhibits particularly good adhesion to metals and thus also to screw connections, and the inventive solid lubricants, i.e., polyethylene wax and synthetic paraffins, can be very well integrated into a polymer matrix, resulting in homogeneous and thermally and mechanically very resistant sliding properties. In a particularly preferred embodiment of the invention, the polymer resin is a mixture of phenoxy and epoxy resins and / or the crosslinker is a phenolic resin; i.e., most preferably, the polymer matrix is ​​the reaction product of phenoxy resin, epoxy resin, and phenolic resin. In a preferred embodiment, resins made of glycidyl ethers and polyphenols are provided as the epoxy resin, particularly those with a molecular mass of 3,500 to 12,000 g / mol.Long-chain polyhydroxy ethers or phenoxypolymers are preferably used as phenoxy resins, more preferably with an average molecular weight of 32,000 to 60,000 g / mol, particularly preferably 52,000 g / mol. Phenol-formaldehyde resins, especially butyl-etherified formaldehyde resins, are preferred as phenol resins.

[0039] According to the invention, suitable additives for the coating are those commonly used in coatings. Coating additives in the sliding coating according to the invention are preferably selected from the group consisting of dispersing agents, wetting agents, deaerating agents, leveling agents, and defoamers.

[0040] The lacquer additives in the sliding lacquer according to the invention are preferably selected from the group consisting of dispersing additives, rheology additives, deaerators, leveling agents and defoamers. Fillers and / or pigments are also used.

[0041] In general, paint additives must be adapted to both the substances used in the paint, such as solid lubricants and fillers, and the application area, for example, the substrate to be coated. Rheological additives and anti-settling agents can also be added as needed.

[0042] Suitable fillers for the sliding coatings of the invention include conventional fillers such as insoluble silicate compounds, also in the form of dioxide or silica derivatives, carbonates, phosphates and sulfates, carbon blacks, and various metal oxides, preferably with particle sizes predominantly in the fine powder range. Generally, usable fillers and pigments are mentioned, for example, in Fillers, Detlef Gysau, 3rd revised edition, 2014, Vincentz Network.

[0043] According to the invention, corrosion protection pigments are understood to be pigments that protect against corrosion. These corrosion protection pigments can also be designed as active corrosion protection pigments. Active corrosion protection pigments intervene in the corrosion processes at the interface between a metallic substrate and a coating through chemical reactions. Their corrosion-inhibiting effect is based on changes in the valence of soluble pigment components. Zinc phosphates, zinc-aluminum phosphates, and calcium-modified silica gel are preferred corrosion protection pigments, as described, for example, in the BASF Handbook of Coating Technology, Prof. Dr. Artur Goldschmidt and Dr. Hans-Joachim Streitberger, 2014, Vincentz Network. The preferred pigment-binder ratio, determined according to DIN EN ISO 23811, is 0.83 to 1.12, and particularly preferably 0.85 to 1.00.The preferred pigment volume concentration according to DIN EN ISO 23811 is 32.5% to 40.0% and particularly preferably 33% to 36.5%.

[0044] Furthermore, pigments, metallic effect pigments (including aluminum flakes), and / or dyes are used in the lubricant according to the invention. Carbon black is preferably used as a pigment according to the invention. Depending on the manufacturing process and post-treatment, pigment particles of varying fineness and thus varying dispersibility are obtained. In principle, other coloring pigments and dyes are also suitable, provided that they are temperature-stable during curing. Preferred metallic effect pigments for a silver-colored lubricant are micaceous iron oxide, pearlescent pigments, and zinc pigments; more preferably, aluminum pigments in lamellar form, particularly as leafing or non-leafing types. The average particle size is preferably from 5 µm to 55 µm, more preferably from 10 µm to 35 µm. Preferred metallic effect pigments for a black lubricant are bone black, iron oxide black, iron manganese black, or spinel black.Carbon black pigments are preferably used, particularly with a particle size of 10 nm to 50 nm, and especially preferably 15 nm to 35 nm. Preferred dyes are metal complexes, for example dyes of the type Cl solvent black 27 or Cl solvent black 29.

[0045] The lubricant used in the inventive sliding varnish is a mixture of polyethylene wax and synthetic paraffin. In particular, high- and ultra-high-molecular-weight polyethylene with high density and / or a particle size of 1–20 pm is preferred as the polyethylene wax. Polyethylene wax in combination with synthetic paraffin, also known as Fischer-Tropsch wax, has, according to the invention, achieved a very advantageous lubricating effect.

[0046] In a preferred embodiment, a further addition of 0.5 to 2.5 wt.% polyamide powder, particularly preferably PA12 with an average particle size dso of about 5 pm, more preferably with a melting temperature of 170 - 185°C, can optionally increase the abrasion resistance of the sliding coating and lead to an even more constant friction behavior under mechanical and thermal stress and in particular the thermal dynamic driving test.

[0047] The preferred total amount of lubricant, comprising polyethylene wax, synthetic paraffins, and optionally polyamide powder, based on the total weight of the dried sliding varnish, is 5.5 to 9.0 wt.% and particularly preferably 6.0 to 8.5 wt.%.

[0048] A sliding lacquer within the meaning of the invention is understood to be a dry sliding lacquer, i.e., a dried sliding lacquer, i.e., a sliding lacquer after drying. Drying preferably takes place at a temperature > 60 °C, particularly preferably 90–110 °C for about 1–30 min, preferably 5–10 min. After drying, the thinning agent and solvent have evaporated. This is followed by curing, preferably at a temperature of 140–250 °C, particularly preferably 180–215 °C for about 20–60 min, preferably 30–45 min, during which the polymer matrix chemically cross-links. Before drying, the sliding lacquer is referred to as a wet sliding lacquer or a sliding lacquer dispersion, i.e., it comprises thinning agent and / or solvent, in particular organic solvents.

[0049] The weight percentages of the components of the inventive sliding lacquer are, as indicated, based on the total weight of the sliding lacquer, i.e., they are based on the total weight of the dried sliding lacquer or the sliding lacquer in the dried state. In a preferred embodiment of the invention, the sliding lacquer for screw fasteners, in particular for wheel bolts and wheel nuts, comprises 35–47 wt.% of a polymer matrix.

[0050] 30 - 45 wt.% fillers and / or corrosion protection pigments,

[0051] 5.0 - 10 wt.% paint additives,

[0052] 5.0 - 10 wt.% pigments, dyes and / or metallic effect pigments,

[0053] 2.0 - 8.0 wt.% polyethylene wax and

[0054] 0.8 - 3.0 wt.% synthetic paraffins, where the weight percentages are based on the total weight of the lubricant, i.e. the weight percentages are based on the total weight of the lubricant in the dried state.

[0055] The lubricant may further preferably comprise 1.0 - 10.0 wt.% wetting and / or dispersing additives, more preferably 6.5 - 9.0 wt.% wetting and / or dispersing additives.

[0056] In a further preferred embodiment of the invention, the sliding lacquer for screw fasteners comprises

[0057] 40 - 45 wt% polymer matrix,

[0058] 35 - 40 wt.% fillers and / or corrosion protection pigments,

[0059] 5.0 - 9.0 wt.% paint additives,

[0060] 5.0 - 8.0 wt.% pigments, dyes and / or metallic effect pigments,

[0061] 3.5 - 7.0 wt.% polyethylene wax and

[0062] 1.3 - 2.5 wt.% synthetic paraffins, where the weight percentages are based on the total weight of the lubricant in the dried state.

[0063] In particular, the above preferred compositions enable the achievement of exceptionally consistent friction behavior both during and after multiple assembly processes, as well as during and after thermal and, in particular, thermodynamic tightness testing. In a preferred embodiment of the invention, the sliding coating comprises < 1 wt.%, more preferably < 0.5 wt.%, more preferably < 0.1 wt.%, and most preferably < 0.01 wt.% polyfluoroalkyl substances (PFAS), based on the total weight of the sliding coating.

[0064] For the purposes of this invention, synthetic paraffins are understood to be synthetically produced paraffins, as is customary, in contrast to so-called petroleum-based paraffins. Synthetic paraffins are generally produced using the Fischer-Tropsch process. They preferably comprise saturated hydrocarbons (alkanes), preferably predominantly unbranched alkanes, of the molecular formula C nH2n+2. The number for n is preferably between about 12 and 100. A distinction is made between low-viscosity paraffins, high-viscosity paraffins, hard paraffins and microwaxes.

[0065] Synthetic paraffins with a melting point of 80–125°C are preferred, particularly preferably 112–120°C. Saturated hydrocarbons are preferred for the synthetic paraffins. Microwaxes are particularly preferred. The chain lengths are preferably up to 75 carbon atoms. The enthalpy of fusion is preferably between 200 and 240 kJ / kg.

[0066] For the purposes of this invention, polyethylene wax is understood to mean, as is customary, polyethylenes that have a wax-like character. So-called oxidized polyethylene wax can also be used as polyethylene wax. Preferred polyethylene waxes are polymerization products that are produced from ethylene gas using a metallocene catalyst. Depending on the degree of polymerization, crystallization, and branching of the polymer, different forms of high-density polyethylene are formed. According to the invention, the density is preferably 0.93 to 0.98 g / cm³. 3It is further preferred that the polyethylene wax is in particle form (micronized polyethylene wax), more preferably with an average particle size dso of 3–12 pm. The average molar mass of the polyethylene in the polyethylene wax is preferably 200,000 g / mol to 7,500,000 g / mol, more preferably 300,000 g / mol to 6,500,000 g / mol, and particularly preferably 500,000 g / mol to 6,000,000 g / mol. The molar mass is preferably the average molar mass, in particular the number-average molar mass. The melting point of the polyethylene wax is preferably 110 - 145 °C, more preferably 120 - 143 °C, also more preferably 120 - 140 °C, more preferably 130 - 142 °C, even more preferably 135 - 142 °C, most preferably 138 - 142 °C, in particular 138 - 140 °C.

[0067] Preferred polyamide waxes are polymers (polycondensation products) of aliphatic diamines of the molecular formula H₂N-(CH₂)x-NH₂ and aliphatic dicarboxylic acids of the formula HOOC-(CH₂)y-COOH with x = 8–17, preferably 11–14, and / or y = 4–14, preferably 6–12, and / or polycondensation products of aminocarboxylic acids or corresponding lactams with the molecular formula H₂N-(CH₂)X-COOH, with x = 8–20, preferably x = 10–15. The polyamide wax can preferably also be in particle form (micronized). The micronized polyamide wax preferably has a particle size dso of about 4 to 6 pm and / or a melting point of 170 to 185°C.

[0068] The described synthetic paraffins and polyethylene waxes, in combination with the described binder matrix including all substances contained therein, enable particularly consistent friction conditions to be achieved both during multiple assembly and during and after thermal and thermodynamic tightness testing. An optional addition of polyamide wax, e.g., micronized PA-12, can further improve the resistance of the dried and chemically cross-linked sealant to mechanical and thermal stresses.

[0069] In a preferred embodiment of the invention, the mean layer thickness of the sliding lacquer is 1–50 pm, preferably 3–30 pm, and particularly preferably 6–18 pm. For the purposes of the invention, the mean layer thickness is understood to be the arithmetic mean of at least three, preferably five, measured layer thicknesses. For this purpose, the layer thickness is measured at at least three, preferably five, randomly selected locations, for example, under a microscope in a section perpendicular to the surface. The arithmetic mean of the measured layer thicknesses is then determined.

[0070] The synthetic paraffins and polyethylene waxes are preferably in particle form. The mean particle size dso is preferably 1–20 pm, more preferably 3–12 pm, and particularly preferably 4–10 pm. dgs is preferably 3–25 pm, more preferably 10–20 pm, and particularly preferably 12–18 pm. The PA-12 powder optionally used may preferably have a mean particle size dso of 1–12 pm and particularly preferably 4–7 pm.

[0071] Within the scope of the present invention, the dso value is the particle size at which 50% of the particles are smaller in volume than the dso value and 50% of the particles are larger in volume than the dso value. This applies analogously to the dgs value, where 98% of the particles are smaller in volume than the dgs value and 2% of the particles are larger in volume than the dgs value. The d-values ​​according to the invention are determined by laser diffraction using a dispersion unit, in accordance with DIN ISO 13320.

[0072] To produce the sliding coating according to the invention, polymer resin (binder) dissolved in a solvent, preferably an organic solvent, is dispersed with the addition of dispersing additives, fillers, and pigments and / or dyes, including corrosion protection pigments. If necessary, defoamers and anti-settling agents can also be added.

[0073] In the next step, fine dispersion is preferably carried out, e.g., using a stirred mill or bead mill, to achieve complete wetting and thus an optimal and stable pigment distribution within the liquid phases through strong shear action. The liquid coating material is then completed by adding the appropriate crosslinking agents (hardeners), as well as additives and solid lubricants. If required, rheology additives and further solvents can also be added. The total amount of solvent is typically about 25–75 wt.%, preferably 30–70 wt.%, and particularly preferably 45–65 wt.%, based on the total mass of the sliding coating to be applied, i.e., the sliding coating in its wet state (dry coating dispersion).

[0074] In its wet state, the inventive sliding coating for screw fasteners, in particular wheel fasteners and especially wheel bolts, comprises 28–80 wt.% polymer matrix, 10.5–30 wt.% fillers and corrosion protection pigments, 5–18 wt.% coating additives, pigments and / or dyes or metallic effect pigments such as aluminum pigments, 0.4–1.8 wt.% synthetic paraffins, 1.2–5.0 wt.% polyethylene wax and 25–75 wt.% organic solvent, wherein the weight percentages are based on the total weight of the wet sliding coating (sliding coating dispersion), i.e., the sliding coating which still contains organic solvents before drying and baking.

[0075] For example, the following compositions are preferred for the wet sliding varnish according to the invention (gliding varnish dispersion) (polymer resin and hardener together form a polymer matrix):

[0076] 22 - 60 wt.% polymer resin (binder)

[0077] 7.5 - 20 wt.% hardener (crosslinker)

[0078] 1.5 - 5 wt% dispersing additive

[0079] 3.0 - 15 wt.% fillers

[0080] 3.5–20 wt.% corrosion protection pigments

[0081] 3.5 - 10 wt.% color pigments - carbon black / metallic effect pigments 0.5 - 3 wt.% rheology additive

[0082] 0.4 - 1.8 wt% synthetic paraffins, 1.2 - 5 wt% polyethylene wax

[0083] The remainder consists of 100% by weight organic solvents.

[0084] The following composition is particularly preferred for the wet sliding lacquer according to the invention:

[0085] 25–35 wt.% polymer resin (binder) 8–12 wt.% hardener 1–3 wt.% dispersing additive 3–10 wt.% fillers 5–15 wt.% corrosion protection pigments

[0086] 3.5 - 7.5 wt.% color pigments - carbon black / metallic effect pigments; 0.5 - 3.0 wt.% rheology additive; 0.4 - 1.2 wt.% synthetic paraffins; 1.25 - 3.0 wt.% polyethylene wax; balance to 100 wt.% organic solvents

[0087] The invention also relates to the use of the inventive sliding varnish for coating screw fasteners, in particular nuts and screws for wheel fastening, especially preferably wheel bolts.

[0088] The invention further relates to a screw fastener, preferably for wheel connections, more preferably a wheel bolt, with a sliding lacquer coating, wherein the screw fastener has a surface and a layer of the sliding lacquer according to the invention is applied to at least a part of the surface. Preferably, the screw fastener is a bolt or nut, and in particular, these have a thread, and the layer of sliding lacquer is applied to at least a part of the thread, preferably to the entire thread, and most preferably to the entire surface of the screw fastener. The sliding lacquer preferably has a density of 8 g / m². 2 up to 20 g / m² 2 and especially preferred at 10 g / m² 2 up to 18 g / m² 2 Applied, determined according to DIN EN ISO 10111, based on a dried sliding lacquer. These quantities represent specific thicknesses or material strengths.

[0089] In a preferred embodiment of the invention, a further layer of a zinc-containing layer, preferably a zinc-nickel layer, in particular of Cr-[III]-passivated zinc-nickel, or a zinc-containing dispersion layer, is located on the surface of the screw connection and under the layer of sliding lacquer, and further preferably a further layer of an adhesion promoter is located above it.

[0090] Preferably, the adhesion promoter is a polymer of organofunctional silanes / siloxanes and functionalized, nanoscale SiO₂ particles and / or alkaline earth silica, e.g., 8–10 wt% silane / siloxane polymer and 8–10% lithium silicate, the remainder being 100 wt% demineralized water, hereinafter also referred to as a sealant. Particularly preferably, the adhesion promoter consists of a commercially available film-forming chromium phosphate-zinc citric acid complex, hereinafter referred to as a film-forming passivation. In both cases, the layer thickness of the adhesion promoter is 0.3 to 3.0 µm, and particularly preferably 0.5 to 1.5 µm.

[0091] The invention also relates to a method for manufacturing a screw connection with a sliding lacquer coating, comprising the steps

[0092] Providing a screw fastener with a surface, dispersing a polymer resin as well as fillers and / or corrosion protection pigments, paint additives, as well as pigments, dyes and / or metallic effect pigments in a solvent,

[0093] Addition of a crosslinking agent, polyethylene wax and synthetic paraffin and optionally further additives to the dispersion, mixing to form a sliding lacquer dispersion, optionally application of a zinc-containing layer to at least part of the surface of the screw fastener, optionally application of an adhesion promoter,

[0094] Applying at least one layer of the sliding lacquer dispersion to at least part of the surface of the screw fastener, drying the layer and

[0095] Baking of the layer at a temperature of 140 to 250 °C.

[0096] The zinc-containing layer is preferably an electroplated zinc layer, a zinc-iron layer, a zinc-nickel layer, or a zinc-containing dispersion layer (especially zinc pigments with aluminum and / or magnesium components). A zinc-nickel layer is particularly preferred, especially with a nickel content of 12-15 wt.%, based on the total weight of the layer. Even more preferably, it can be provided with an adhesion-promoting layer (sealant), for example, with an adhesion-promoting, film-forming passivation.

[0097] In a preferred embodiment of the method according to the invention, the surface of the screw fastener is cleaned, in particular degreased, before the application of a first layer. This can be done, for example, by alkaline degreasing with a sodium hydroxide solution plus surfactants, followed by pickling with acid, for example inhibited hydrochloric or sulfuric acid, and / or subsequent alkaline electrolytic degreasing, wherein the metallic screw fastener is anodically connected.

[0098] In a further preferred embodiment of the method according to the invention, the coating is spun off before drying, preferably at a lateral acceleration of 25 - 30 G (1 G corresponds to the acceleration due to gravity of 9.81 m / s²). 2 ).

[0099] Drying is preferably carried out at a temperature > 60 °C, particularly preferably 90–110 °C, for about 1–30 min, preferably 5–10 min. Curing to crosslink the polymer matrix is ​​preferably carried out at a temperature of 140–250 °C, preferably 160–220 °C, and particularly preferably 180–215 °C, for a duration of 20–60 min, preferably 30–45 min. The coated screw fastener is then cooled.

[0100] The screw connection is preferably made of a metallic material, in particular steel.

[0101] The application, drying, and curing process can be carried out once, or the application, drying, and curing steps can be repeated, optionally several times, so that the lubricant coating then consists of several individual layers. Preferably, two layers are applied; that is, the steps of applying the lubricant, drying, and curing are repeated once after curing and cooling. In a further preferred embodiment of the method according to the invention, a zinc-nickel layer is first applied to the screw fastener before the lubricant is applied, preferably with a nickel content of 12–15 wt.%, based on the total weight of the zinc-nickel layer. This zinc-nickel layer preferably has an average layer thickness of 5–15 pm, particularly 8–12 pm. Furthermore, passivation and / or the application of an adhesion promoter can preferably take place after the application of the zinc-nickel layer.The adhesion promoter is preferably present in a layer and has a layer thickness of 0.3 - 3 pm, in particular 0.5 - 1.5 pm.

[0102] The invention also relates to the use of the screw connection device according to the invention, in particular the screw connection device for fastening a wheel and in particular the wheel screw according to the invention for fastening a wheel, in particular for fastening a wheel to a vehicle, for example a car or truck.

[0103] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the present invention. The advantages of features or combinations of several features mentioned are merely examples and can have an effect alternatively or cumulatively. The combination of features from different embodiments of the invention or features from different claims may deviate from the chosen cross-references in the claims.

[0104] The invention will be further explained below using an example.

[0105] EXAMPLE

[0106] Performing the thermo-dynamic fixed-seat test:

[0107] Vehicle preparation:

[0108] - New wheel bolts, new wheels

[0109] - Brake discs with zinc coating

[0110] - Wheel hub threads in like-new condition or re-tapped

[0111] - 1-piece suit

[0112] - Tightening torque: 80% of the assembly torque

[0113] - Line markings on screws and rims

[0114] Experimental procedure:

[0115] 1.) 15 braking maneuvers from 70 km / h without steering input

[0116] 2.) 15 braking maneuvers from 70 km / h with sudden left-hand braking

[0117] 3.) Visual inspection of line marking and

[0118] Temperature measurements

[0119] 4.) 15 min slalom (fast driving; max. speed with full braking at the apex)

[0120] 5.) Visual inspection of line marking and

[0121] Temperature measurements 6.) 10 min slalom (fast driving; max. speed with full braking at the apex)

[0122] 7.) Visual inspection of line marking and

[0123] Temperature measurements

[0124] 8.) Measurement of thermal release torque

[0125] 9.) After cooling: Measurement of the release torque

[0126] Evaluation and documentation

[0127] Production of a coated wheel bolt a) Production of the coating of the sliding lacquer

[0128] The manufacturing instructions serve as the basis for producing the coating material. These instructions include the following work steps:

[0129] • Weighing of components: organic solvents 22.0 wt.%

[0130] Polymer resin (epoxy resin) 32.5 wt.%

[0131] Color pigments - carbon black and dyes 2.8% by weight

[0132] Corrosion protection pigments 11 wt.%

[0133] Fillers 4.5% by weight

[0134] Dispersing additive 2.7 wt.%

[0135] • Predispersion / homogenization in a premixer, 20 min.

[0136] • Fine dispersion using a stirred mill (circulation)

[0137] • Completing the approach with further components

[0138] Hardener (phenolic resin) 11.5 wt.% organic solvents 7.7 wt.% rheology additive 1.2 wt.% synthetic paraffins 0.8 wt.% polyethylene wax 1.8 wt.% • Adjusting the viscosity with organic solvent, max. 3 wt.%

[0139] • Quality control, checking the characteristic properties according to the test plan

[0140] • Filling and labeling of the coating material b) Application of the coating to the screw surface

[0141] A coating system with a total of 4-6 layers, preferably 5 layers, is applied to the surface of a wheel bolt:

[0142] An alkaline zinc-nickel layer (approx. 10 pm) is applied to the screw surface, immediately followed by a black passivation layer (approx. 0.2 pm), then an adhesion promoter, a film-forming passivation layer (approx. 1 pm), and immediately above that, two coats of the above-mentioned black sliding lacquer (total 12-18 pm; with a layer weight of approximately 15 g / m²). 2 ).

[0143] To apply these layers, the following work steps are carried out one after the other:

[0144] • Alkaline degreasing 120g / l NaOH 70 - 80 °C

[0145] • HCl mordant inhibits

[0146] • Electrolytic degreasing, parts anodically connected / alkaline

[0147] • Active bath GC CORE 300 alkaline ZnNi (membrane process) 12-15% Ni content

[0148] • Passivation GC PASS 421.1 (black)

[0149] • Layer-forming passivation GC PASS 800

[0150] • Drying at 80°C object temperature

[0151] • Coating 1st layer: sliding lacquer

[0152] • Spin cycle at 30G

[0153] • Pre-dry for 5-10 minutes at 90-110°C

[0154] • Baking time: 30-35 min at 200-210°C • Cooling time: approx. 10 min (part temperature < 35°C)

[0155] • Coating 2nd layer sliding lacquer

[0156] • Spin cycle at 30G

[0157] • Pre-dry for 5-10 minutes at 90-110°C

[0158] • Burn-in for 30-35 minutes at 200-210 °C

[0159] • Cooling zone approx. 10 min (part temperature < 35 °C)

[0160] The lubricant exhibits very good adhesion (DIN EN ISO 2409, cross-cut test GT0) and high corrosion resistance of at least 720h salt spray test DIN EN ISO 9227 without suffering base metal corrosion.

[0161] Furthermore, the sliding varnish exhibits very good media resistance, especially against gasoline E 10, diesel fuel B7, reference engine oil according to TL52185, hydraulic oil TL52146, coolant TL774, brake fluid TL766, tested according to DIN EN ISO 2812-3.

[0162] The lubricant also exhibits very good resistance to wheel cleaners. For this test, the coated fasteners are completely immersed five times in a 6% hydrochloric acid solution for two minutes and then rinsed with tap water. After a two-hour corrosion test according to DIN EN ISO 9227, the visible surface of the fasteners shows no signs of base metal corrosion.

[0163] The sliding coating also exhibits very good corrosion resistance, with more than 480h salt spray test DIN EN ISO 9227 480h without white rust or grey haze (without any visible surface change).

[0164] The excellent corrosion resistance is maintained even after a thermal preconditioning of 96 hours at 180°C and / or a mechanical preconditioning, whereby the fastener is tightened 10 times to the maximum assembly torque using a torque wrench and loosened each time with an impact wrench. In the case of mechanical preconditioning, only the visible surface of the fastener is evaluated after the corrosion stress test.

[0165] Polymer backbone based on epoxy phenolic resin, free phenol content after curing < 0.1%.

[0166] The tribological properties of the above layer, according to the example, satisfy the following conditions:

[0167] • Preload force for initial tightening at 130 Nm torque M14 x 1.5 x 27: 35 < Fv < 65 kN

[0168] • Multiple tightening cycles in original aluminum wheels (with new parts); 20 tightening cycles on original wheel, brake disc without spacer, wheel flange as nut thread. After 10 tightening cycles: M14 x 1.5 x 27; MA 130 Nm: 35 < Fv < 65 kN; After 20 tightening cycles: M14 x 1.5 x 27; MA 130 Nm: 30 < Fv < 65 kN

[0169] • The ratio of the loosening torque at RT to the tightening torque at RT should be greater than 60%, preferably greater than 70%, after the thermo-dynamic tightness test.

[0170] Example: Tightening torque according to functional specification: 104 Nm

[0171] Measured before thermo-dynamic tightness test: 105.5 Nm Measured after thermo-dynamic tightness test (cold loosening torque): 111.5 Nm

[0172] Loosening torque after thermo-dynamic tightness test (cold loosening torque):

[0173] 111.5 Nm

[0174] X > 70% (Preferred) = - x 100%

[0175] Tightening torque before thermo-dynamic fit test = 105.5 Nm

[0176] X = 105.69%

[0177] Thus, the condition >70% is met. • The ratio of the loosening torque at 150°C to the tightening torque at room temperature should be greater than 50%, preferably greater than 60%, after the thermo-dynamic tightness test.

[0178] Example: Tightening torque according to functional specification: 104 Nm

[0179] Measured before thermodynamic tightness test: 106.4 Nm Measured after thermodynamic tightness test (hot loosening torque): 78.9 Nm

[0180] Loosening torque after thermo-dynamic tightness test (hot loosening torque): 78.9 Nm

[0181] X > 60% (Preferred) = - x 100%

[0182] Tightening torque before thermo-dynamic fit test = 106.4 Nm

[0183] X = 74.15%

[0184] That is, the condition >60% is met.

[0185] Further advantages and features of the present invention will become apparent from the following description with reference to the figures. Individual features of the illustrated embodiments can also be used in other embodiments, unless this has been expressly excluded.

[0186] They show:

[0187] Fig. 1: a screw fastener.

[0188] Figure 1 shows a screw fastener 1, which can be a wheel bolt. The screw fastener 1 has a thread 20. Furthermore, the screw fastener 1 has a head 10, which has an inner and / or an outer drive area to allow positive-locking torque transmission to the screw fastener 1. Below the head 10 is the contact surface 30, which is curved. Alternatively, the contact surface 30 can also be conical or spherical. This design also allows for centering, particularly when the screw fastener 1 is a wheel bolt and / or a male screw fastener 1. However, the invention can be applied not only to male fasteners 1 but also to female screw fasteners 1, especially nuts.Between the thread 20 and the contact surface 30 there is a relief groove 32. The sliding lacquer can advantageously be applied to the thread 20 and / or the contact surface 30, or these areas can be coated with the sliding lacquer.

Claims

AMENDED CLAIMS received by the International Bureau on 23 April 2026 (23.04.2026) 1. Sliding lacquer for screw fasteners (1), in particular for wheel bolts and wheel nuts, comprising 30 - 50 wt% of a polymer matrix, 25 - 50 wt.% fillers and / or corrosion protection pigments, 3 - 15 wt.% paint additives, 3 - 15 wt.% pigments, dyes and / or metallic effect pigments, 1.0 - 10.0 wt.% polyethylene wax and 0.5 - 5.0 wt.% synthetic paraffins, wherein the wt.% are based on the total weight of the dried lubricant, characterized in that the polymer matrix is ​​a reaction product of a polymer resin and a crosslinker and the polymer resin is selected from the group consisting of polyamide, polyamide-imide, polyurethane, polyester, acrylate, epoxysilane, epoxysiloxane, phenoxy, epoxy and mixtures thereof and the crosslinker is selected from the group consisting of isocyanate resin, imidazole resin, phenol resin, amine resin and mixtures thereof.

2. Sliding lacquer according to claim 1, characterized in that the sliding lacquer contains < 0.1 wt.%, preferably < 0.01 wt.% polyfluorinated alkyl substances (PFAS), based on the total weight of the sliding lacquer.

3. Lubricating varnish according to claim 1 or 2, characterized in that the synthetic paraffins are saturated hydrocarbons with a melting point of 80 - 125°C and / or the polyethylene wax has a density of 0.93 to 0.98 g / cm³ 3 and has a melting point of 120 - 140°C. 31 AMENDED SHEET (ARTICLE 19) 4. Lubricating lacquer according to one of the preceding claims, characterized in that the synthetic paraffin and / or the polyethylene wax is in particle form, with a mean particle size dso of 3 - 12 pm.

5. Lubricating varnish according to one of the preceding claims, characterized in that the polymer matrix is ​​a reaction product of a polymer resin and a crosslinker and the polymer resin is selected from the group consisting of phenoxy, epoxy and mixtures thereof and the crosslinker is selected from the group consisting of phenolic resin, amine resin and mixtures thereof.

6. Lubricating varnish according to one of the preceding claims, characterized in that the amine resin is a benzoguanamine resin.

7. Sliding lacquer according to one of the preceding claims, characterized in that the sliding lacquer additionally contains 0.5 to 2.5 wt.% polyamide powder, based on the total weight of the dried sliding lacquer.

8. Sliding lacquer according to one of the preceding claims, characterized in that the total amount of polyethylene wax, synthetic paraffins and optional polyamide powder, based on the total weight of the dried sliding lacquer, is 6.0 to 8.5 wt.%.

9. Use of a sliding lacquer according to one of claims 1 - 8 for coating a screw fastener (1 ), in particular a wheel bolt and / or wheel nut. AMENDED SHEET (ARTICLE 19) 10. Screw fastener (1 ) with sliding lacquer coating, wherein the screw fastener (1 ) has a surface, characterized in that a layer of sliding lacquer according to one of claims 1 - 8 is applied to at least a part of the surface.

11. Screw fastener (1) according to claim 10, characterized in that the screw fastener (1) is a wheel bolt or wheel nut having a thread (20) and the layer of sliding lacquer is applied at least to a part of the thread (20).

12. Screw fastener (1 ) according to claim 10 or 11 , characterized in that between the surface of the screw fastener (1 ) and the layer of sliding lacquer there is a further layer containing zinc and optionally a layer of an adhesion promoter above it.

13. A method for producing a screw fastener (1) with a coating of sliding lacquer according to any one of claims 1-8, comprising the steps: a) providing a screw fastener (1); b) dispersing a polymer resin as well as fillers and / or corrosion protection pigments, lacquer additives, as well as pigments, dyes and / or metallic effect pigments in a solvent; c) adding a crosslinker, polyethylene wax and synthetic paraffin and optionally further additives to the dispersion; d) mixing to form a sliding lacquer dispersion; e) optionally applying a zinc-containing layer and optionally applying a layer of an adhesion promoter to at least a part of the surface of the screw fastener; f) applying a layer of the sliding lacquer dispersion to at least a part of the surface of the screw fastener; g) drying the layer; and 33 AMENDED SHEET (ARTICLE 19) h) Baking of the dried layer at a temperature of 140 to 250 °C.

14. Use of a screw fastener (1), in particular a wheel bolt or wheel nut, according to one of claims 10-12 for Fastening of a wheel, in particular for attaching a wheel to a vehicle. AMENDED SHEET (ARTICLE 19)

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