EP3400323B1 - Self-lubricating electrolytically deposited phosphate coating - Google Patents

Description

The present invention relates to a self-lubricating, electrolytically deposited phosphating coating on metallic workpieces comprising stabilized solid lubricants embedded in the phosphating coating and a method for producing the same.

The functionality of metallic workpieces can nowadays be expanded in a targeted manner through a large number of downstream processing steps. In particular, for the modification of the surface properties, industrial processes are provided which are able to change both the aesthetic and the application properties in such a way that more durable and visually more appealing products are available. In addition to abrasive processes such as polishing and grinding, coating processes are preferably used for further processing, in which gaseous, liquid, dissolved or solid substances are used to build up additional, coherent layers on the workpiece. For fast coatings, liquid, predominantly aqueous systems are used, from which dissolved substances can be deposited chemically or electrochemically. Examples of electrolytic coating processes are chromating, galvanic galvanizing and phosphating, the latter being used when the corrosion resistance is increased or else cold massive forming of the metallic base body is intended. During the cold forging of metallic workpieces, the surface pressure creates a high level of friction between the tool and the workpiece, which can lead to local welding of the surfaces sliding on each other and subsequent damage of the workpiece and / or the tool. In order to reduce the friction, a phosphating layer is applied before the deformation, which, in combination with the application of further lubricants, usually contributes to a reduction in the friction in the subsequent deformation process. The sliding effect of the phosphate layer itself is only of secondary importance; it is more important that this layer has a crystalline structure with high porosity, which can absorb up to 13 times more lubricant, for example oil, compared to untreated metal surfaces. Solid lubricants also adhere better to a phosphated metal surface than to bare steel. By means of this combination treatment of phosphating and subsequent oil / lubricant coating, the forces that occur during cold forming can be reduced so that a reproducible machining process is made possible.

One possible method for phosphating metal layers is named for example DE 103 48 251 A1 . Electrolytic depositions from acidic aqueous solutions are disclosed which contain at least zinc and phosphate ions and are carried out with the simultaneous application of direct current. Simultaneously with the deposition of the phosphating layer, an electrolytic deposition of zinc takes place in the same electrolyte, the current density being greater than -5 A / dm ² .

Another method for phosphating a metal layer by electrolytic deposition from acidic aqueous solutions that contain at least zinc and phosphate ions is in the DE 10 2006 035 974 A1 disclosed. This document discloses metal layers which are covered with a zinc (zinc alloy) / zinc phosphate layer, foreign particles having been incorporated into the zinc (zinc alloy) / zinc phosphate layer.

The DE 164 492 7 discloses a process for the production of particles containing dry lubricant which are to be incorporated into metal coatings to be applied by electroplating in workpieces exposed to sliding friction, by placing them in the electrolyte introduces and during the galvanic deposition of the metal coating against the surface of the workpiece connected as cathode, with finely divided, powdered dry lubricant, optionally together with silicon carbide or aluminum oxide particles as wear-resistant particles in a synthetic resin solution or in a silicate solution, which optionally as a conversion into poorly soluble compounds effecting substances are admixed with lime water, aluminum chloride or sulfuric acid, is stirred in, that the solvent is driven out of the mixture by evaporation and the residue is mechanically comminuted to the desired particle size.

Another method for double phosphating, optionally also with the aid of a polymer in the phosphating solution, is in the DE 197 81 959 B4 describe. After an initial phosphating, the phosphated workpiece is bathed in a bath of 8.5 to 100 Ca ⁺¹ g / l; 0.5 to 100 Zn ²⁺ g / l, 5 to 100 PO4 ³ g / l; 0 to 100 NO ³ g / l; 0 to 100 CIO ³ g / l and 0 to 50 F ^- or Cl ^- g / l, to which polymers and solid lubricants are added to improve the friction properties of the second phosphating layer.

Furthermore, the DE 19 781 959 B4 and the GB 20 28 830 A with phosphated metal surfaces.

The previous methods of applying solid lubricants to phosphating layers are complex and expensive and, in particular, do not allow high coating speeds to be achieved or integrated solid lubricant particles to be provided within phosphating layers. It is therefore the object of the following invention to eliminate the disadvantages of the prior art and, in particular, to provide self-lubricating phosphating layers and processes for their production.

The features of the method according to the invention and the features of the phosphating layers according to the invention are reproduced in the independent claims. The The dependent claims, however, reproduce preferred configurations of the method and the layers.

According to the invention, an electrolytically deposited phosphating layer is at least comprising the elements zinc and phosphorus on a metallic workpiece, the phosphating layer having solid lubricant particles stabilized by hydrocolloids, the stabilized solid lubricant particles being at least partially embedded in the phosphating layer, the hydrocolloids being selected from the group comprising polyamines , polyimines as well as their quaternary salts, polyvinyl pyrrolidones, polyvinyl pyridines, collagen, gelatin, Chitosanhydrolysat, keratin hydrolyzate, casein hydrolyzate, Amidopektine, as well as their copolymers and / or mixtures thereof, and the solid lubricant particles metal and ammonium salts are selected from the group comprising saturated fatty acids, MoS ₂ , h-BN, WS ₂ , graphite, oxidized and fluorinated graphite, PTFE, nylon, PE, PP, PVC, PS, PET, PUR, clay, talc, TiO ₂ , mullite, CuS, PbS, Bi ₂ S ₃ , CdS or mixtures thereof. Surprisingly, it has been found that phosphating layers with the above features can be reproducibly deposited on workpieces and even high deposition speeds lead to coherent layers which can be processed without any problems in subsequent cold forming steps without further application of lubricant or lubricant. This finding is particularly astonishing because it would have been expected that the incorporation of solid lubricant particles into the phosphating layer would lead to a significant loss of quality of the deposited layer. These solid particles can lead to the fact that the layer is mechanically destabilized or that no contiguous (coherent) layers are formed at all. In addition, it is surprising that these high-quality layers with built-in lubricant particles can be obtained within conventional bath compositions and parameters. In particular, it is possible to produce the layers according to the invention with the same or similar deposition rates, so that there are no or only minimal losses in the efficiency of the baths. Furthermore, it is advantageous that the incorporation of the lubricant particles the additional step of applying lubricant or lubricant / lubricant particles is omitted, so that the workpieces phosphated according to the invention can be fed to mechanical cold forming without further process steps. Without being bound by theory, the high-quality deposition and the resulting stability of the phosphating layers, which are additionally laden with solid lubricant, result from the presence of the hydrocolloids in the phosphating bath. These hydrocolloids are apparently able to stabilize the solid lubricants in the solution in the form of coacervates by attaching themselves to the solid lubricant particles. These addition complexes can apparently contribute to a better distribution of the solid lubricant particles in the solution. In addition, these coacervates appear to be able to In comparison to the non-stabilized particles, the layer structure is stored more quickly and less disruptively in the phosphating layer. The result is a more uniform and coherent phosphating layer structure, which is mechanically more stable compared to layers with non-stabilized particles.

A phosphating layer in the context of the invention is an electrolytically deposited zinc phosphate layer on a metallic workpiece. In principle, this can be applied using known methods and is widely used, for example, to protect low-alloy steels from corrosion. In a pH-controlled precipitation reaction, zinc phosphate crystals (hopeite) are deposited on the component surface during phosphating by exceeding its solubility product. This can be achieved, for example, by pickling the base metal (e.g. Fe → Fe ²⁺ + 2e ^- ), with the electrons being released serving to reduce protons. This shifts the pH of the aqueous bath solution into a neutral to basic range and exceeds the solubility product of the zinc phosphate. The layer that forms is generally approx. 2 - 20 µm thick and can have a coverage of the component surface of approx. 90% to 95%, sometimes up to 100%.

The phosphating layer applied according to the invention is deposited electrolytically. This can be done either by applying a direct current or by applying a pulsed direct current. Usual currents are in the range of 0.1 and 250 mA / cm ² and the bath temperatures can be selected in a range from 20 to 90 ° C. The temperature is preferably between 25 ° C and 80 ° C. The coating duration, ie the time in which a current flows through the workpiece and metal ions are deposited from the solution on the workpiece, can be freely determined and can expediently be between a few seconds, for example 1 second, and several minutes, such as 5 minutes. The coating time is expediently the desired as a function of the concentration of the ions to be deposited Layer thickness and the workpiece geometry selected. The treatment times of modern systems for electrolytic galvanizing and phosphating of steel strips are between 90 and 120 m / min. There are deposition times in the range of up to 5 seconds. In general, treatment times of 0.5 to 5 seconds can be used in this coating situation. In the most common applications, the layer thickness of the phosphating layer can be from 5 µm to 15 µm.

Metallic workpieces can be equipped with the phosphating coatings according to the invention. The concept of a metallic workpiece includes one-, two- or three-dimensional structures made of usually low-alloy steels. These layers can also be used on stainless steels and other noble and base metals, such as Iron, Al, Ti, Cu, Ni, or their alloys, as well as hot-dip galvanized materials can be attached. The term one-dimensional structure includes, for example, wires, the two-dimensional structure, for example, strips or sheets, and the three-dimensional structure, for example, more complex shapes such as bearing shells. The metallic workpieces can be constructed in one or more layers. In particular, it is also within the meaning of the invention that the phosphating layer having stabilized solid lubricant particles can also be applied to a “normal” layer that is not provided with stabilized solid lubricant particles.

The solid lubricant particles are stabilized by hydrocolloids both in the solution and most likely in the phosphating layer. The hydrocolloids preferably have a chain-like structure made up of individual, successive building blocks. The hydrocolloids are able to form viscous solutions in water by swelling with the accumulation of water on the hydrocolloid structure. The hydrocolloids which can be used according to the invention can be built up from one and the same (homopolymer) or else from different building blocks (heteropolymer). The hydrocolloids can have a weight of preferably 1000 to 1,000,000 Da. This particle size has proven to be a effective interaction with the solid lubricant particles proved to be particularly suitable. Larger particles can interfere with the incorporation of the lubricant particle into the layer and smaller hydrocolloid sizes can only lead to insufficient stabilization of the lubricant particle and thus to mechanically unstable phosphating layers. The weight of the hydrocolloids can expediently be determined using gel permeation techniques using defined reference samples. Suitable hydrocolloids are especially the water-soluble, ie swellable, hydrocolloids. Examples include phenol sulfonate / formaldehyde condensates, polyvinyl alcohol, polyethers, polyacrylates and methacrylates, polyacrylamides, polyvinylamines, polyamines, polyimines and their quaternary salts, polyvinylpyrrolidones, polyvinylpyridines, polyvinylphosphonates and their copolymers, as well as natural hydrocolloids such as collagen, gelatine, and chysate, keratin hydrolysates , Casein hydrolyzate, guar, pectins, agar-agar, starch and modified starch, cellulose derivatives such as carboxyalkyl cellulose or cellulose ethers, or mixtures and copolymers thereof.

The solid lubricant particles are stabilized by means of the hydrocolloids. This means that the solid lubricant particles in the aqueous solution come into contact with the swollen polymeric hydrocolloids and interact with them on the surface. In principle, it is possible here for the solid lubricant particle to be stabilized both through interaction with the side chains or through contact with the backbone of the hydrocolloid. Without being bound by theory, the hydrocolloid particles are adsorbed on the lubricant surface, with a polymer layer being at least partially formed around the solid lubricant. This adhesive hydrocolloid layer is able to mechanically stabilize the lubricant particle in the solution and in the phosphating layer. In a preferred embodiment, it is possible for the deposited phosphating layer to have a proportion of 15 to 60% by weight, more preferably 20 to 40% by weight, of solid lubricant particles. By means of this proportion of lubricant, sufficient intrinsic lubrication can be achieved for many applications with simultaneous Maintain good mechanical properties of the phosphating layer. The size of the stabilized solid lubricant particles can be in the range between 0.5 μm and 3 μm, preferably between 1.0 μm and 2 μm. The size of the stabilized lubricant particles can be determined by dynamic laser light scattering or by means of microscopic methods. The weight ratio of solid lubricant particles to hydrocolloid can be varied within a wide range without departing from the area of effective stabilization of the solid particle. The ratio can expediently be varied from 100: 1 up to 1: 100. This means that an effective stabilization of the lubricant particle can also be achieved if only part of its surface is covered by the hydrocolloids which can be used according to the invention.

As a result of the electrolysis, the stabilized lubricant particles are, at least partially, embedded in the phosphating layer. According to the invention, the stabilized solid lubricant particles are not only deposited on the surface or in the pores of the phosphating layer, but rather are also incorporated into the phosphating layer. As a result, a stabilized solid lubricant particle can be completely or partially surrounded by zinc phosphate. However, it is also possible that not every stabilized solid lubricant particle is permanently built into the layer, but that some of the stabilized solid lubricant particles are only bound adsorptively on the workpiece surface. According to the invention, after a single immersion of the workpiece without additional mechanical movement in demineralized water at 20 ° C for 1 minute, at least 60% by weight, preferably 80% by weight and furthermore preferably at least 90% by weight of the stabilized solid lubricant particles remain non-washable within the layer . The total amount of stabilized solid lubricant particles can be determined by dissolving the material and subsequent quantitative elemental analysis. The amount of stabilized solid lubricant particles bound only on the surface can result from a determination of the concentration of the stabilized solid lubricant particles in the washing water. Alternatively, the proportion of the washed / unwashed coated workpieces can also be determined using quantitative X-ray methods such as ED-RFX.

In a first embodiment, the hydrocolloid can be a nitrogen-containing hydrocolloid. In particular, the nitrogen-containing hydrocolloids seem to be able to form stable coacervates with the solid lubricant particles. These special coacervates enable a particularly adequate stabilization of the solid lubricant particles in the solution and ensure that the particles are correctly incorporated into the phosphating layer. In particular, the nitrogen-containing hydrocolloids can therefore contribute to an effective separation of the solid lubricant particles without the separation of the other phosphating constituents being impaired in a quality-reducing manner. Without being bound by theory, the cationic charge of the N-hydrocolloid in the prevailing bath conditions also seems to favor this separation behavior, with both the stabilization of the lubricant particles in the bath and the incorporation of these in the phosphating layer being positively influenced . The result is a mechanically flexible and sufficiently stable encapsulation of the solid lubricants, which do not disturb the layer structure of the phosphating layer on the workpiece and can easily be released in a cold forming process under mechanical stress. In principle it is possible that the hydrocolloid has the nitrogen either in the side chains, on the hydrocolloid backbone or both and. The hydrocolloids can preferably have nitrogen atoms both within the chain and on the side groups. The nitrogen can also form different organic functional groups known to the person skilled in the art.

In a further embodiment, the hydrocolloids can be selected from the group comprising polyamines, polyimines and their quaternary salts, polyvinylpyrrolidones, polyvinylpyridines, collagen, gelatin, chitosan hydrolyzate, keratin hydrolyzate, casein hydrolyzate, amidopectins, and copolymers and / or mixtures thereof. This group of nitrogen-containing hydrocolloids in particular leads in combination with the most common solid lubricant particles to particularly strong interactions and thus to a particularly suitable mechanical stabilization of the solid lubricant particles and / or the resulting phosphating layer. Without being bound by theory, this may be due in particular to the molar ratio between nitrogen and the other constituents of the polymers mentioned and the swelling behavior of these hydrocolloids with the aqueous bath composition. The hydrocolloid can preferably have between 5 and 40 mol%, furthermore preferably between 10 and 30 mol% nitrogen. These amounts of nitrogen in the hydrocolloid can lead to a sufficient swelling behavior with development of the hydrocolloid in the phosphating solution and thus contribute to a quick and effective interaction with the solid lubricant particles.

In a further embodiment, the hydrocolloids can be selected from the group of vegetable or animal nitrogen-containing hydrocolloids consisting of gelatin, chitosan hydrolyzate, keratin hydrolyzate, casein hydrolyzate or mixtures thereof.

In a further embodiment, the hydrocolloid can be gelatin with a molecular weight of greater than or equal to 1000 Da and less than or equal to 100,000 Da. Gelatin with a molecular weight in the range specified above can form particularly stable complexes with solid lubricant particles. This can be due in particular to the fact that gelatine swells particularly well in acid phosphating baths and forms an almost completely unfolding chain. This unfolded chain is in turn able to interact particularly effectively with the solid lubricant particles and to stabilize them mechanically. Another reason for the special stabilization could be that gelatine has nitrogen in both the basic structure and the side chains. This division of the nitrogen allows the hydrocolloid chain to bind to the solid lubricant particles particularly quickly and effectively. Preferred molecular weight ranges for the gelatin are furthermore between greater than or equal to 5000 Da and less than or equal to 75,000 Da, more preferably between greater than or equal to 10000 Da and less than or equal to 50,000 Da. High quality phosphating layers can be obtained within these areas.

In an additional characteristic of the phosphating layer, the solid lubricant particles from the group comprising metal and ammonium salts of saturated fatty acids, MoS ₂ , h-BN, WS ₂ , graphite, oxidized and fluorinated graphite, PTFE, nylon, PE, PP, PVC, PS PET, PUR, clay, talc, TiO ₂ , mullite, CuS, PbS, Bi ₂ S ₃ , CdS or mixtures thereof can be selected. These compounds can be sufficiently stabilized by the nitrogen-containing hydrocolloids in the chemical environment of a phosphating bath and built into a phosphating layer in sufficient quantities without the structure of the layer being excessively disturbed. Coherent, stable phosphating layers are obtained which are provided with a sufficient amount of lubricant so that further lubricant application in the course of further mechanical processing can be dispensed with. The lubricant particles are advantageously present in particulate form. In particular, the particles without stabilization can have a size (greatest distance within the lubricant particle) of greater than or equal to 10 nm and less than or equal to 10 μm, preferably greater than or equal to 25 nm and less than or equal to 5 μm, further preferably greater than or equal to 30 nm and less than or equal to 2.5 µm. These particle sizes can be incorporated without destroying the basic structure of the phosphating layer and provide sufficient quantities of lubricant. The size of the lubricant particles can be determined using methods known to those skilled in the art, such as laser light scattering.

Furthermore, in a preferred characteristic, the solid lubricant particles can consist of MoS ₂ and have a platelet-shaped geometry. Molybdenum sulphide lubricant particles can be stabilized particularly effectively by hydrocolloids and provide installation kinetics that can be controlled over a wide range. In this way, sufficient quantities of lubricant particles can be built into the layer deposits even with short live contact times. An extremely minor disruption of the layer structure the phosphating layer also results in particular when the particles have a platelet-shaped geometry. This geometry can lead to a higher loading of the phosphating layer with lubricant particles and can guarantee an immediate lubricating effect during mechanical processing. The latter can be the case because the lubricant particles appear to be built into the phosphating layer with their elongated sides parallel to the workpiece surface. The MoS ₂ flakes then have a flaky geometry when the particle dimensions are within the following limits: an average length selected from a range with a lower limit of 0.1 μm and an upper limit of 2 μm and an average width a range with a lower limit of 0.1 μm and an upper limit of 2 μm and an average height selected from a range with a lower limit of 2 nm and an upper limit of 50 nm.

1. a) Bereitstellen eines metallischen Werkstückes,
2. b) Eintauchen des metallischen Werkstückes in eine wässrige Elektrolytlösung mindestens umfassend Zink, Phosphationen, Festschmierstoffpartikel und Hydrokolloide, wobei die Hydrokolloide ausgewählt sind aus der Gruppe umfassend Polyamine, Polyimine sowie deren quaternäre Salze, Polyvinylpyrrolidone, Polyvinylpyridine, Kollagen, Gelatine, Chitosanhydrolysat, Keratinhydrolysat, Caseinhydrolysat, Amidopektine, sowie deren Copolymere und/oder Mischungen daraus, und die Festschmierstoffpartikel ausgewählt sind aus der Gruppe umfassend Metall- und Ammoniumsalze gesättigter Fettsäuren, MoS₂, h-BN, WS₂, Graphit, oxidiertes und fluoriertes Graphit, PTFE, Nylon, PE, PP, PVC, PS PET, PUR, Ton, Talk, TiO₂, Mullit, CuS, PbS, Bi₂S₃, CdS oder Mischungen daraus,
3. c) Leiten eines elektrischen Stromes durch das metallische Werkstück zur Abscheidung einer Phosphatierungsschicht auf dem Werkstück und
4. d) optional, Nachbehandeln der elektrolytisch abgeschiedenen Phosphatierungsschicht.

Also according to the invention is a method for producing a phosphating layer having stabilized solid lubricant particles, which comprises at least the steps:

1. a) Provision of a metallic workpiece,
2. b) Immersing the metallic workpiece in an aqueous electrolyte solution at least comprising zinc, phosphate ions, solid lubricant particles and hydrocolloids, the hydrocolloids being selected from the group comprising polyamines, polyimines and their quaternary salts, polyvinylpyrrolidones, polyvinylpyridines, collagen, gelatin, chitosan hydrolyzate, keratin hydrolyzate, keratin hydrolyzate , Amido pectins, as well as their copolymers and / or mixtures thereof, and the solid lubricant particles are selected from the group comprising metal and ammonium salts of saturated fatty acids, MoS ₂ , h-BN, WS ₂ , graphite, oxidized and fluorinated graphite, PTFE, nylon, PE , PP, PVC, PS PET, PUR, clay, talc, TiO ₂ , mullite, CuS, PbS, Bi ₂ S ₃ , CdS or mixtures thereof,
3. c) conducting an electric current through the metallic workpiece to deposit a phosphating layer on the workpiece and
4. d) optionally, post-treatment of the electrolytically deposited phosphating layer.

By means of this process, coherent phosphating layers can be produced which are provided with a sufficient amount of lubricant and do not require any additional lubricant additive in the context of mechanical aftertreatment. This process can also be operated with high current densities, so that high deposition speeds and thus high layer thicknesses can be achieved with short process times. The process can be easily combined with the common phosphating pre-treatment steps such as alkaline cleaning with or without surfactant and with or without intermediate rinsing.

The process is preferably an immersion process, the bath composition can furthermore have accelerators such as urea, nitrates, chlorates, bromates, hydrogen peroxide, ozone, organic nitro bodies, peroxy compounds, hydroxylamine, nitrite nitrate, nitrate perborate or mixtures thereof. The coating solution is preferably an emulsion with emulsion droplets in the sub-micron range. The zinc phosphate solution can be adjusted to an acidic pH range using acids. Rinsing with demin, for example, are possible follow-up treatments. Water or post-passivation with chromic acid, chromic acid / phosphoric acid solution or organic post-passivation with poly (vinylphenol).

Preferred bath parameters can result from: - temperature ≥ 20 and ≤ 70 ° C - PH value ≥ 0.5 and ≤ 2.5 - Zn concentration ≥ 10 and ≤ 70 g / L - phosphate concentration ≥ 35 and ≤ 70 g / L - lubricant particle concentration ≥ 2 and ≤ 25 g / L - hydrocolloid concentration ≥ 0.01 and ≤ 5 g / L - wetting agent concentration ≥ 0.5 and ≤ 5 g / L - current density ≥ 10 and ≤ 20 A / dm ² - contact time ≥ 1 and ≤ 15 sec

In a preferred embodiment of the method, the stabilized phosphating layer containing solid lubricant particles can be deposited on a workpiece which has a phosphating layer with the elements ZnXP on the surface, X being selected from the group comprising Fe, Ni, Ca, Mn. The deposition of further metals from the group mentioned above can contribute to an additional mechanical stabilization of the phosphating layer. In this way, the proportion of lubricant can be increased so that particularly effective, self-lubricating workpieces can be obtained.

In an additional characteristic, the current-carrying contact time of a surface element of the workpiece with the aqueous electrolyte solution can be greater than or equal to 1 second and less than or equal to 100 seconds. The method according to the invention is particularly suitable for being able to deposit a sufficiently thick phosphating layer on a metal workpiece within short process times. For this reason, the live contact time, i.e. the time in which the workpiece is immersed in the bath and the workpiece is flowed through, can be kept very short. This is particularly important for wires and tapes which are drawn through the coating baths at high speeds. This time period expressly does not include the time during which components of the bath are still on the surface of the workpiece, but no actual coating (deposit) takes place.

Within a further aspect of the method, the weight per unit area of the deposited, stabilized solid lubricant particles containing phosphating layer, determined according to DIN EN ISO 3892, can be greater than or equal to 0.5 g / m ² and less than or equal to 10 g / m ² . In addition to the advantages already mentioned above, the incorporation of stabilized solid lubricant particles can lead to significantly lower surface weights compared to the usual phosphating processes. In this way, for example, costs for the use of coating metals can also be saved. These weights per unit area provide sufficiently coherent and firmly adhering layers, which can only be partially destroyed after significant mechanical stress and, as a result, release the lubricant. Preferably, the weight per unit area can also be greater than or equal to 0.75 g / m ² and less than or equal to 8 g / m ² and furthermore preferably greater than or equal to 1.0 g / m ² and less than or equal to 5.0 g / m ² .

In a further, preferred aspect, the aqueous electrolyte solution can additionally contain an anionic, cationic, amphoteric or non-ionic wetting agent in one concentration of greater than or equal to 0.1 and less than or equal to 10 g / l. The addition of this amount of wetting agent can lead to the stabilized solid lubricant particles being distributed more homogeneously in the bath solution and overall a homogeneous application to the metallic workpiece is achieved. Furthermore, the wetting agents can contribute to increasing the coating speed. This can contribute to a reduction in the overall process times.
In a further embodiment of the method, the phosphating solution can have a ratio of free acid to total acid (FSV, free acid ratio) of 2.5 and 10 and more preferably of 5.0 and 8 8.0. This ratio seems to lead to a particularly effective stabilization of the solid lubricant particles by the hydrocolloids. Without being bound by theory, the zeta potential of both the solid lubricant particles and the hydrocolloids can be modified by this ratio in such a way that both particularly good stabilization of the particles in the solution and particularly effective incorporation of the stabilized particles into the Phosphating layer results. The person skilled in the art is familiar with the dimensional analytical determination of the above-mentioned ratio.

Also within the meaning of the invention are metallic, coated workpieces, at least comprising a self-lubricating phosphating layer having solid lubricant particles stabilized by hydrocolloids.

In a further embodiment of the method, it can also be used for treating draw-peeled workpieces, in particular draw-peeled wires. It can in particular be provided that the draw-peeled surface of the workpiece is electrochemical, e.g. by pickling, or mechanically, e.g. by blasting, brushing or grinding, is activated before a coating according to the invention takes place.

With regard to further advantages and features of the method described above, explicit reference is hereby made to the explanations in connection with the system according to the invention. Features according to the invention and advantages of the layers according to the invention should also be applicable to the method according to the invention and should be considered disclosed and vice versa.

Examples: Example 1:

A phosphated cold heading wire is produced, a steel wire with a diameter of 10 mm being coated with a phosphating solution of the following composition for about 10 seconds Zinc: 40 g / L Phosphate: 40 g / L Acid ratio of free acid to total acid: 7.5 PH value: 1.2 gelatin 0.2 g / L (hydrocolloid) Wetting agent (BASF Crafol AP 261) 0.2 g / L Molybdenum disulfide particles (5 µm) 6.0 g / L is pulled. The temperature of the bath is approx. 55 ° C and the strength of the direct current is approx. 12 A / dm ² . A phosphating layer with an average thickness of 4-8 g / m ^{2 is} deposited, which has embedded molybdenum sulfide particles. The phosphated cold heading wire is rinsed with water and then drawn in one step to a diameter of 7 mm at a speed of 0.06 m / sec. Pulling takes place without the addition of any other lubricant. The wire can be adjusted with a constant final diameter pull without problems and there is no breakage of the wire or any other loss of quality.

Example 2

A phosphated cold heading wire is produced, a cold heading wire with a diameter of 10 mm for approx. 2 seconds through a phosphating solution of the following composition: Zinc: 45 g / L Phosphate: 40 g / L Acid ratio of free acid to total acid: 6.5 PH value: 1.2 Polyethyleneimine G 35 BASF 0.1 g / L (hydrocolloid) Wetting agent (BASF Lutensol ON 110) 0.5 g / L Boron nitride particles 1 µm (Hebofill 410) 5.5 g / L is pulled. The other bath parameters correspond to those of Example 1. A phosphating layer with an average thickness of 6 g / m ^{2 is} deposited which has embedded boron nitride particles. The phosphated cold heading wire is rinsed with water and then drawn in one step to a diameter of 7 mm. Pulling takes place without the addition of any other lubricant. The wire can be drawn with a constant final diameter without problems and there is no tearing of the wire or any other loss of quality.

Claims (11)

1. Method for producing a phosphating layer comprising stabilized solid lubricant particles, at least comprising the steps of:

   a) providing a metallic workpiece;

   b) immersing the metallic workpiece in an aqueous electrolyte solution comprising at least zinc, phosphate ions, solid lubricant particles and hydrocolloids, wherein the hydrocolloids being selected from the group consisting of polyamines, polyimines and their quaternary salts, polyvinylpyrrolidones, polyvinylpyridines, collagen, gelatin, chitosan hydrolyzate, keratin hydrolyzate, casein hydrolyzate, amidopectins and their copolymers and/or mixtures thereof, and wherein the solid lubricant particles consist of or include substances which are selected from the group consisting of metal and ammonium salts of saturated fatty acids, MoS₂, h-BN, WS₂, graphite, oxidized and fluorinated graphite, PTFE, nylon, PE, PP, PVC, PS, PET, PUR, clay, talc, TiO₂, mullite, CuS, PbS, Bi₂S₃, CdS or mixtures thereof;

   c) passing an electrical current through the metallic workpiece for depositing a phosphating layer on the workpiece; and

   d) optionally aftertreating the electrolytically deposited phosphating layer.
2. Method according to claim 1, wherein the phosphating layer comprising stabilized solid lubricant particles is deposited on a workpiece which comprises a further phosphating layer with the elements ZnXP on the surface, wherein X being selected from the group consisting of Fe, Ni, Ca, Mn.
3. Method according to claim 1 or 2, wherein the current-carrying contact time of a surface element of the workpiece with the aqueous electrolyte solution is greater than or equal to 1 second and less than or equal to 100 seconds.
4. Method according to any one of claims 1 to 3, wherein the basis weight of the deposited phosphating layer comprising stabilized solid lubricant particles, determined according to DIN EN ISO 3892, is greater than or equal to 0.5 g/m² and less than or equal to 10 g/m².
5. Method according to any one of claims 1 to 4, wherein the aqueous electrolyte solution additionally comprises an anionic, cationic, amphoteric or nonionic wetting agent in a concentration of greater than or equal to 0.1 and less than or equal to 10 g/l.
6. Method according to any one of claims 1 to 5, wherein the metallic workpiece is made of a low-alloy steel, a stainless steel, iron, aluminum, titanium, copper, nickel, alloys comprising iron, aluminum, titanium, copper or nickel, or hot-dip galvanized materials.
7. Method according to any one of claims 1 to 6, wherein the workpiece is a workpiece produced by means of draw-peeling.
8. Method according to claim 7, wherein the surface of the workpiece is pretreated mechanically or electrochemically, in particular activated prior to being immersed in the coating bath.
9. Electrolytically deposited phosphating layer obtained by a method according to any one of claims 1 to 8, at least comprising the elements zinc and phosphorus on a metallic workpiece, characterized in that the phosphating layer comprises solid lubricant particles stabilized by hydrocolloids, wherein the stabilized solid lubricant particles are at least partially embedded in the phosphating layer, wherein the hydrocolloids being selected from the group consisting of polyamines, polyimines and their quaternary salts, polyvinylpyrrolidones, polyvinylpyridines, collagen, gelatin, chitosan hydrolyzate, keratin hydrolyzate, casein hydrolyzate, amidopectins and their copolymers and/or mixtures thereof, and the solid lubricant particles consist of or include substances which are selected from the group consisting of metal and ammonium salts of saturated fatty acids, MoS₂, h-BN, WS₂, graphite, oxidized and fluorinated graphite, PTFE, nylon, PE, PP, PVC, PS, PET, PUR, clay, talc, TiO₂, mullite, CuS, PbS, Bi₂S₃, CdS or mixtures thereof.
10. Phosphating layer according to claim 9, wherein the hydrocolloid is gelatin with a molecular weight greater than or equal to 1000 Da and less than or equal to 100000 Da.
11. Phosphating layer according to claim 9 or 10, wherein the solid lubricant particles consist of MoS₂ and have a platelet-shaped geometry.