EP3390690B1 - Passivating solution for passivating a surface of a metal part - Google Patents

Passivating solution for passivating a surface of a metal part Download PDF

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Publication number
EP3390690B1
EP3390690B1 EP17710122.7A EP17710122A EP3390690B1 EP 3390690 B1 EP3390690 B1 EP 3390690B1 EP 17710122 A EP17710122 A EP 17710122A EP 3390690 B1 EP3390690 B1 EP 3390690B1
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EP
European Patent Office
Prior art keywords
passivating solution
concentration
layer
conversion layer
passivating
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EP17710122.7A
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German (de)
French (fr)
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EP3390690B8 (en
EP3390690A1 (en
Inventor
Michael Grabowski
Tommy Wetzel
Michael Korte
Guillermo DE CASTRO LODOSA
Sannakaisa Virtanen
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Audi AG
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Audi AG
Friedrich Alexander Univeritaet Erlangen Nuernberg FAU
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
    • C23C22/08—Orthophosphates
    • C23C22/22—Orthophosphates containing alkaline earth metal cations
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/68—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous solutions with pH between 6 and 8

Definitions

  • the invention relates to a passivation solution for forming a conversion layer for the surface of the metal component according to the preamble of claim 1.
  • metal components especially light metal components
  • vehicle bodies can be made of mixed construction, for example from light metal and sheet steel parts, in order to achieve a weight reduction.
  • aluminum or magnesium materials or alloys thereof can be used as the light metal.
  • paint subsurface migration and filiform corrosion are frequently occurring damage patterns.
  • pickling, passivation and the application of an organic coating is common practice.
  • the commercial coatings only partially offer the necessary protective effect against self-corrosion, filiform corrosion and/or paint creep.
  • the high potential difference must be regarded as promoting corrosion.
  • a generic method for passivating a surface of a metal component is known.
  • a conversion layer containing calcium phosphate is produced on the surface of the metal component in a passivation step using an aqueous passivation solution.
  • the Conversion Layer shows oxides and hydroxides as well as carbonates of the component material and the passivation solution.
  • the passivation that takes place in this way can be upstream of a process chain for painting vehicle bodies, as can be seen from the DE 196 30 289 C2 is known.
  • a method for surface treatment of a surface of a component is known, the material of which is a magnesium alloy.
  • a nickel coating with a uniform thickness can be produced with the method.
  • a dosing solution for an anodic oxidation of magnesium or magnesium alloys is known.
  • a method for coating a light metal component made of a magnesium alloy is known.
  • the object of the invention is to provide a passivation solution for forming a conversion layer for the surface of a metal component, in which simple and improved passivation is made possible compared to the prior art.
  • the passivation solution for the formation of the conversion layer has exactly one substance acting as a chelate complexing agent (ie chelate ligand). This results in a layer formation mechanism, described later, in which the conversion layer formed has fewer cracks than in the prior art.
  • the passivation solution contains a large number of different organic substances that function as chelate complexing agents (i.e. chelate ligands). This large number of different chelating complexing substances can compete with one another during the formation of the conversion layer, so that the mechanism of formation of the layer is impaired, which can lead to the crack structure in the conversion layer.
  • chelate complexing agents i.e. chelate ligands
  • the passivation solution ie the coating electrolyte
  • these substances are substituted by precisely one substance which acts as a chelate complexing agent.
  • a directed layer growth takes place, in which the layer formation mechanism is initiated by the only chelate complexing substance contained.
  • the layer formation mechanism is therefore not affected by other competing substances that can also act as chelating complexing agents.
  • the conversion layer is thus covered with a closed, low-crack layer morphology formed, whereby its protective effect is improved.
  • any suitable substance can be used as the chelating agent.
  • An organic substance with optionally deprotonated functional groups with one or more free electron pairs can preferably be used as the chelate complexing agent, ie for example OH end groups, COOH end groups, NH 2 end groups or the like.
  • an organic acid or its salts, an amino acid or a suitable vitamin can be used as the organic substance.
  • the organic acid contained in the passivation solution can be a tartaric acid, an acetic acid or L-arginine.
  • the substance acting as a chelate complexing agent can preferably be contained in the passivation solution with a concentration in the range of 1-20 mmol/l.
  • carboxylic acids organic acids
  • other possible groups of chelating complexing agents are also: alcohols, phenols, naphthols, enols, thiols, sulfonic acid, phosphoric acid esters, phosphonic acid.
  • the chelate complexing substance contained in the passivation solution (tartaric acid as an example below) enables a flawless layer formation mechanism for the formation of the conversion layer compared to the prior art:
  • the tartaric acid acts as a chelate complexing agent, in which the Ca 2 + ions are complexed in the respective tartaric acid molecule, with the formation of a chelate complex.
  • the Ca 2+ ions are bound to the tartaric acid molecule by electrostatic attraction.
  • the chelate complex is temporarily physically and reversibly adsorbed to the metallic component surface via any deprotonated functional groups, i.e. for example via OH end groups.
  • the Ca 2+ ions bound in the chelate complex are therefore also transported to the metallic component surface. There it reacts with the phosphates dissolved in the passivation solution and forms the conversion layer containing calcium phosphate. Subsequently, the chelating agent (ie the chelating ligand) is desorbed and the same process can take place again.
  • the passivation solution according to the invention By means of the passivation solution according to the invention, a further reduction in contact corrosion currents with aluminum, steel, zinc, carbon fibers or CFRP can take place compared to the above prior art. Furthermore, there is an additional increase in the penetration resistance. The higher the penetration resistance of the conversion layer, the lower the corrosion currents. The penetration resistance is therefore inversely proportional to the corrosion currents. In addition, the passive behavior of the conversion layer is increased in comparison to the above prior art, due to the essentially closed, low-crack layer structure of the conversion layer.
  • the metal component designed with the passivated surface can be used across all sectors.
  • the metal component can be used in the medical field.
  • the metal component can optionally be used in the automotive sector, namely hidden from view inside the vehicle or as an external part that is visible from the outside.
  • the metal component can be implemented as a vehicle interior display frame, an assembly part, a chassis part or a component part of a seat frame structure.
  • the passivation solution produces a compact coating containing calcium phosphate and aluminum hydroxide/oxide with amino acids.
  • the layer morphology is essentially closed, that is to say at least with few cracks.
  • a component material made of magnesium results in a compact coating containing calcium phosphate and magnesium hydroxide/oxide, the layer morphology of which is also essentially closed and has few cracks.
  • the passivation solution contains MgSO 4 .7H 2 O with a concentration of between 100 and 400, in particular 200 mg/l.
  • Ca 2+ and/or PO 4 3- ions are also built into the conversion layer as fragments to support layer formation.
  • the passivation layer can contain calcium phosphates.
  • the conversion layer has carbonate-containing components.
  • the passivation solution can contain NaHCO 3 . Carbonate formation is also dependent on any CO 2 that may have been added.
  • the passivation solution can contain at least exactly the following components in combination: NaCl with a concentration between 5000 and 8000, in particular 6400 mg/l; and or KCl with a concentration between 300 and 500, in particular 400 mg/l, NaH2PO4 _ with a concentration between 100 and 170, in particular 124 mg/l, and/or CaCl 2 with a concentration between 170 and 300, in particular 200 mg/l NaHCO 3 with a concentration between 3500 and 4500, in particular 3700 mg/l MgSO4.7H2O _ with a concentration between 100 and 400, in particular 200 mg/l chelating agents with in particular 1 to 20 mmol/l
  • the passivation reaction according to the invention can take place at a pH of about 7. In this case, the coating reaction proceeds slowly. Alternatively, the coating reaction can also take place in the acidic range.
  • the coating reaction can be accelerated by increasing the temperature, reducing the pH and/or by polarizing and/or increasing the partial pressure of CO 2 .
  • the coating process can preferably be accelerated with the help of a pH value reduction (pH from 1 to 5) and with the help of a temperature increase from normal room temperature by 15° to 80°C.
  • the metal component can be a vehicle part, which is first pretreated with the passivation solution according to the invention to form the conversion layer.
  • the conversion layer of the component can be covered with at least one further layer in a subsequent coating process.
  • the coating process has a first coating step, in which a KTL layer, ie an organic protective layer, is formed.
  • a KTL layer ie an organic protective layer
  • a powder coating is then applied in a further coating step.
  • This is done in a powder coating process under applied DC voltage.
  • a process-reliable coating the above-mentioned closed, low-crack layer morphology is of particular importance. On the one hand, this ensures a high protective effect of the conversion layer. On the other hand, sufficient residual electrical conductivity through the conversion layer is ensured in the dipping process and in the powder coating process.
  • the metal component for example as an outer part on the visible side
  • the metal component can be joined to the not yet painted body shell in a single joining process.
  • the body-in-white, together with the light metal component mounted on it, is then subjected to a conventional body painting process.
  • This means that the body shell is primed using the immersion method.
  • the body shell provided with the primer is then taken to another coating station, in which a KTL process takes place.
  • the KTL process is followed by a continuous furnace in which the KTL layer is burned in at high temperatures.
  • a conventional automotive paint structure is then applied in a further coating station, which is also baked at high temperature in a subsequent drying step.
  • the metal component mounted on the body shell is already pre-coated with a layer structure, namely with the conversion layer, the KTL layer and the powder coating.
  • the metal component is thus electrically insulated, so that the KTL layer electrically applied in the body-in-white painting process no longer sticks, while the conventional automotive paint structure can be applied easily to the metal component that has already been coated.
  • the layer structure 1 of a paint coating on the surface 25 of a body component 3 is shown as an example in a greatly enlarged partial sectional view.
  • the body component 3 is made of light metal, for example aluminum, magnesium or an alloy thereof.
  • the layer structure 1 has a conversion layer 5 directly on the workpiece surface 25 of the light metal component 3, which serves for passivation and corrosion protection.
  • the conversion layer 5 is covered by a KTL layer 6 .
  • a powder coating 7 is formed on this, on which a conventional automotive, multi-layer paint structure 9 (in Fig. 1a shown in one layer for reasons of clarity) is applied. How from the Fig. 1a further shows that the conversion layer 5 has a substantially closed layer morphology with few cracks.
  • the conversion layer 5 is also formed in such a way that sufficient residual conductivity is provided between a KTL immersion bath and the light metal material of the component 3 in a KTL coating process, which will be described later.
  • the 1 as well as the others Figures 2 to 7 , are prepared for easier understanding of the invention. Therefore, the figures are only roughly simplified representations that do not represent a realistic layer structure 1. Thus, the conversion layer 5 actually has a layer thickness that is in the ⁇ m range.
  • the passivation solution contains at least the following main components: NaCl with 6400 mg/l KCl with 400 mg/l NaH2PO4 _ with 124 mg/l CaCl 2 with 200 mg/l NaHCO 3 with 3700 mg/l MgSO4.7H2O _ with 200 mg/l chelating ligand between 1 and 20 mmol/l
  • NaCl and KCl in the passivation solution are used to activate the metal surface 25.
  • the components NaH 2 PO 4 and CaCl 2 support the coating process by incorporating the Ca 2+ and PO 4 3- ions into the conversion layer 5.
  • the tartaric acid causes the following based on the Figures 1b and 1c described layer formation mechanism for the formation of the conversion layer 5. This is how the tartaric acid works in a first process step ( Fig. 1b ) as a so-called chelate complexing agent, in which the Ca 2+ ions coordinated in the passivation solution are complexed in the respective tartaric acid molecule, forming a chelate complex 8 ( Fig. 1b ). In the chelate complex 8, the Ca 2+ ions are attracted by electrostatic attraction (in the Figures 1b and 1c indicated by dashed lines).
  • the chelate complexing agent alternative to tartaric acid, for example also amino acids/vitamins
  • a second process step ( 1c ) The chelate complex 8 is attached via functional groups, that is, for example via OH end groups, to the Surface 25 of the metal component 3 is briefly physically and reversibly adsorbed (in the 1c indicated by a single arrow).
  • the Ca 2+ ions bound in the chelate complex 8 are therefore also transported to the surface 25 .
  • a reaction occurs with the phosphates dissolved in the passivation solution (in the 1c indicated by a double arrow) and to form the conversion layer 5 containing calcium phosphate.
  • the chelate complexing agent ie the chelate ligand
  • the same process can take place again.
  • the tartaric acid (or another suitable substance) is preferably contained in the passivation solution as the sole chelate complexing agent.
  • a directed layer growth takes place, in which preferably only the tartaric acid acts as a chelating substance.
  • the stratification mechanism initiated by the tartaric acid is therefore not affected by other competing substances that can also act as chelating complexing agents.
  • the conversion layer 5 can be formed with a preferably closed, low-crack layer morphology. The conversion layer 5 therefore has an improved protective effect compared to conversion layers with crack structures.
  • tartaric acid is used as the sole chelating agent.
  • the invention is not limited to this exemplary embodiment.
  • the conversion layer 5 according to the invention also has carbonate-containing layer components. These are provided in the passivation solution by the components NaHCO 3 and CO 2 (from the atmosphere).
  • the passivation solution according to the invention is therefore an aqueous treatment liquid whose pH is in the range of about 7 or in the acidic range.
  • the passivation preferably takes place in the immersion bath at room temperature.
  • the treatment time depends on the set pH value, the process temperature and, if necessary, an additional polarization as well as the required nominal thickness of the coating.
  • the component 3 is fed to a rinsing/drying process.
  • the above coating process can be accelerated by reducing the pH to a value of 1 to 5 and/or by increasing the temperature by 15 to 80°C.
  • the component 3 coated with the conversion layer 5 is in the present application in the further process sequence (according to the 3 ) in a coating station 17 with a KTL layer 6 (ie an organic protective layer).
  • KTL coating is carried out using the immersion method, in which an electrical DC voltage is applied between the body 15 and the immersion bath, as a result of which the paint particles dissolved in the immersion bath are attracted to the component 3 and adhere uniformly there. Additionally required pre- or post-treatment steps are omitted for the sake of easier understanding of the invention.
  • a downstream drying station 18 the component 3 runs through a continuous furnace at a predetermined conveying speed, in which the KTL layer 6 is baked at process temperatures in the range of 180° C., for example. Then, in process step II, a powder coating is carried out in a coating station 20, in which the layer 7 ( 1 ) is applied to component 3.
  • the paint particles are transported to the grounded component 3 by an electrostatic field from live spike heads. This is followed by a baking process in a continuous furnace in a further station 19 .
  • the light metal component 3 is joined as a visible-side vehicle exterior part in a joining process (for example gluing and/or screwing) to a body shell 15 that has not yet been painted.
  • the body shell 15 is in a continuous process in a body painting plant (see 4 ) promoted.
  • the body shell 15 provided with the primer is then fed to a further coating station 29 in which a KTL process takes place.
  • the KTL process 29 is also followed by a continuous furnace 31 in which the coating is baked at high temperature.
  • a further coating station 33 a conventional automotive four-layer paint structure 9 is applied, which is then subjected to a baking process 35.
  • the Indian 4 The body painting process shown is carried out with a light metal component 3 that has already been precoated.
  • the light metal component 3 is electrically insulated, so that the KTL layer applied in the body-in-white painting process no longer sticks, whereas the conventional automotive paint structure 9 (i.e. a four-layer structure) can easily be applied to the powder coating 7 of the metal component 3.
  • the light metal component 3 is shown in different process steps. So is in the figure 5 the light metal component 3 is shown with a cleaned and exposed metallic surface 25 . In the 6 the light metal component 3 is shown after passivation and rinsing or drying has taken place. Accordingly, the conversion layer 5 is applied to the surface 25 of the light metal component. In the 7 the light metal component 3 is shown after the KTL process has taken place.
  • the conversion layer 5 can also remain on the light metal component 3 as the sole layer (ie in a single-layer structure without additional intermediate and cover layers).

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Description

Die Erfindung betrifft eine Passivierungslösung zur Bildung einer Konversionsschicht für die Oberfläche des Metallbauteils nach dem Oberbegriff des Anspruchs 1.The invention relates to a passivation solution for forming a conversion layer for the surface of the metal component according to the preamble of claim 1.

Der Einsatz von Metallbauteilen, insbesondere von Leichtmetallbauteilen, ist branchenübergreifend gängige Praxis. Speziell im Fahrzeugbau können beispielhaft Fahrzeugkarosserien im Mischbau zum Beispiel aus Leichtmetall- und Stahlblechteilen gefertigt werden, um eine Gewichtsreduzierung zu erzielen. Beispielhaft können als Leichtmetall Aluminium- oder Magnesiumwerkstoffe oder Legierungen davon eingesetzt werden. Bei im Mischbau gefertigten Fahrzeugkarosserien besteht die Gefahr von Kontaktkorrosion zwischen den Leichtmetallbauteile (aus Magnesium oder Aluminium) und den Stahl-Bauteilen. Vor allem Lackunterwanderungen und Filiformkorrosion sind häufig auftretende Schadensbilder. Zum Schutz der Leichtmetallbauteile ist ein Beizen, eine Passivierung sowie die Applikation einer organischen Beschichtung gängige Praxis. Die kommerziellen Beschichtungen bieten jedoch nur zum Teil die notwendige Schutzwirkung gegen Eigenkorrosion, Filiformkorrosion und/oder Lackunterwanderung. Vor allem bei Kontakt von Stahl mit Magnesium ist der hohe Potentialunterschied als korrosionsfördernd zu betrachten.The use of metal components, especially light metal components, is common practice across all sectors. Especially in vehicle construction, for example, vehicle bodies can be made of mixed construction, for example from light metal and sheet steel parts, in order to achieve a weight reduction. For example, aluminum or magnesium materials or alloys thereof can be used as the light metal. In the case of vehicle bodies manufactured in mixed construction, there is a risk of contact corrosion between the light metal components (made of magnesium or aluminum) and the steel components. Above all, paint subsurface migration and filiform corrosion are frequently occurring damage patterns. To protect the light metal components, pickling, passivation and the application of an organic coating is common practice. However, the commercial coatings only partially offer the necessary protective effect against self-corrosion, filiform corrosion and/or paint creep. Especially when steel comes into contact with magnesium, the high potential difference must be regarded as promoting corrosion.

Aus der DE 10 2014 005 444 A1 ist ein gattungsgemäßes Verfahren zur Passivierung einer Oberfläche eines Metallbauteils bekannt. In dem Verfahren wird in einem Passivierungsschritt unter Verwendung einer wässrigen Passivierungslösung auf der Oberfläche des Metallbauteils eine kalziumphosphathaltige Konversionsschicht erzeugt. Die Konversionsschicht weist Oxide und Hydroxide sowie Karbonate des Bauteil-Werkstoffes und der Passivierungslösung auf. Die so erfolgte Passivierung kann einer Prozesskette zum Lackieren von Fahrzeugkarosserien prozesstechnisch vorgelagert werden, wie sie aus der DE 196 30 289 C2 bekannt ist.From the DE 10 2014 005 444 A1 a generic method for passivating a surface of a metal component is known. In the method, a conversion layer containing calcium phosphate is produced on the surface of the metal component in a passivation step using an aqueous passivation solution. The Conversion Layer shows oxides and hydroxides as well as carbonates of the component material and the passivation solution. The passivation that takes place in this way can be upstream of a process chain for painting vehicle bodies, as can be seen from the DE 196 30 289 C2 is known.

Bei dem oben skizzierten Schichtbildungsmechanismus wird eine Konversionsschicht erzeugt, die eine schollenförmige Schichtmorphologie mit Rissstrukturen aufweist. Dies führt zu einer Reduzierung der Schutzwirkung der Konversionsschicht. Zudem weist die aus der DE 10 2014 005 444 A1 bekannte Passivierungslösung einen äußerst komplex aufgebauten Beschichtungselektrolyten auf.In the case of the layer formation mechanism outlined above, a conversion layer is produced which has a lump-like layer morphology with crack structures. This leads to a reduction in the protective effect of the conversion layer. In addition, the DE 10 2014 005 444 A1 known passivation solution has an extremely complex coating electrolyte.

Aus der WO 2015/015524 A ist ein Verfahren zur Oberflächenbehandlung einer Oberfläche eines Bauteils bekannt, dessen Werkstoff eine Magnesiumlegierung ist. Mit dem Verfahren kann eine Nickelbeschichtung mit gleichmäßiger Dicke erzeugt werden. Aus der DE 37 15 663 A1 ist eine Andosier-Lösung für eine anodische Oxidation von Magnesium oder Magnesium-Legierungen bekannt. Aus der JP 2009-228087 ist ein Verfahren zum Beschichten eines Leichtmetallbauteils aus einer Magnesium-Legierung bekannt.From the WO 2015/015524 A a method for surface treatment of a surface of a component is known, the material of which is a magnesium alloy. A nickel coating with a uniform thickness can be produced with the method. From the DE 37 15 663 A1 a dosing solution for an anodic oxidation of magnesium or magnesium alloys is known. From the JP 2009-228087 a method for coating a light metal component made of a magnesium alloy is known.

Aus der EP 2 392 693 A1 ist ein Verfahren und eine Lösung zur Passivierung von Magnesiumbauteilen, insbesondre Bauteile für Automobile, bekannt.From the EP 2 392 693 A1 a method and a solution for the passivation of magnesium components, in particular components for automobiles, is known.

Die Aufgabe der Erfindung besteht darin, eine Passivierungslösung zur Bildung einer Konversionsschicht für die Oberfläche eines Metallbauteils bereitzustellen, bei dem im Vergleich zum Stand der Technik eine einfache sowie verbesserte Passivierung ermöglicht ist.The object of the invention is to provide a passivation solution for forming a conversion layer for the surface of a metal component, in which simple and improved passivation is made possible compared to the prior art.

Die Aufgabe ist durch die Merkmale des Patentanspruches 1 gelöst.The object is solved by the features of claim 1.

Bevorzugte Weiterbildungen der Erfindung sind in den abhängigen Ansprüchen offenbart.Preferred developments of the invention are disclosed in the dependent claims.

Gemäß dem Patentanspruch 1 weist die Passivierungslösung für die Bildung der Konversionsschicht genau eine als Chelatkomplexbildner (das heißt Chelatligand) wirkende Substanz auf. Dadurch ergibt sich ein später beschriebener Schichtbildungsmechanismus, bei dem die gebildete Konversionsschicht im Vergleich zum Stand der Technik rissärmer ist.According to patent claim 1, the passivation solution for the formation of the conversion layer has exactly one substance acting as a chelate complexing agent (ie chelate ligand). This results in a layer formation mechanism, described later, in which the conversion layer formed has fewer cracks than in the prior art.

Untersuchungen haben ergeben, dass eine Ursache für die Rissstruktur in der Konversionsschicht darin liegen kann, dass die Passivierungslösung eine Vielzahl unterschiedlicher organischer Substanzen enthält, die als Chelatkomplexbildner (das heißt Chelatliganden) funktionieren. Diese Vielzahl unterschiedlicher Chelatkomplexbildner-Substanzen können bei der Konversionsschicht-Bildung zueinander in Konkurrenz stehen, so dass der Schichtbildungsmechanismus beeinträchtigt wird, was zu der Rissstruktur in der Konversionsschicht führen kann.Investigations have shown that one reason for the crack structure in the conversion layer may be that the passivation solution contains a large number of different organic substances that function as chelate complexing agents (i.e. chelate ligands). This large number of different chelating complexing substances can compete with one another during the formation of the conversion layer, so that the mechanism of formation of the layer is impaired, which can lead to the crack structure in the conversion layer.

Vor diesem Hintergrund ist es bevorzugt, wenn die Passivierungslösung (das heißt der Beschichtungselektrolyt) nicht mehr eine Vielzahl von Substanzen enthält, die beim Beschichtungsprozess als Chelatkomplexbildner funktionieren können. Erfindungsgemäß werden diese Substanzen durch genau eine als Chelatkomplexbildner wirkende Substanz substituiert. Auf diese Weise erfolgt ein dirigiertes Schichtwachstum, bei dem der Schichtbildungsmechanismus von der einzig enthaltenen Chelatkomplexbildner-Substanz eingeleitet wird. Der Schichtbildungsmechanismus wird daher nicht durch andere konkurrierende Substanzen beeinträchtigt, die ebenfalls als Chelatkomplexbildner wirken können. Die Konversionsschicht wird dadurch mit einer geschlossenen, rissarmen Schichtmorphologie ausgebildet, wodurch dessen Schutzwirkung verbessert ist.Against this background, it is preferred if the passivation solution (ie the coating electrolyte) no longer contains a large number of substances that can function as chelate complexing agents in the coating process. According to the invention, these substances are substituted by precisely one substance which acts as a chelate complexing agent. In this way, a directed layer growth takes place, in which the layer formation mechanism is initiated by the only chelate complexing substance contained. The layer formation mechanism is therefore not affected by other competing substances that can also act as chelating complexing agents. The conversion layer is thus covered with a closed, low-crack layer morphology formed, whereby its protective effect is improved.

Als Chelatkomplexbildner können beliebige geeignete Substanzen verwendet werden. Bevorzugt kann als Chelatkomplexbildner eine organische Substanz mit gegebenenfalls deprotonierten funktionellen Gruppen mit einem oder mehreren freien Elektronenpaaren verwendet werden, das heißt zum Beispiel OH-Endgruppen, COOH-Endgruppen, NH2-Endgruppen oder dergleichen. Als organische Substanz kommt zum Beispiel eine organische Säure bzw. deren Salze, eine Aminosäure oder ein geeignetes Vitamin infrage. Exemplarisch kann die in der Passivierungslösung enthaltende organische Säure eine Weinsäure, eine Essigsäure oder L-Arginin sein. Die als Chelatkomplexbildner wirkende Substanz kann bevorzugt mit einer Konzentration im Bereich von 1-20 mmol/l in der Passivierungslösung enthalten sein. Mögliche weitere Gruppen von Chelatkomplexbildnern sind neben Carbonsäuren (organische Säuren) ebenso: Alkohole, Phenole, Naphthole, Enole, Thiole, Sulfonsäure, Phosphorsäureester, Phosphonsäure.Any suitable substance can be used as the chelating agent. An organic substance with optionally deprotonated functional groups with one or more free electron pairs can preferably be used as the chelate complexing agent, ie for example OH end groups, COOH end groups, NH 2 end groups or the like. For example, an organic acid or its salts, an amino acid or a suitable vitamin can be used as the organic substance. By way of example, the organic acid contained in the passivation solution can be a tartaric acid, an acetic acid or L-arginine. The substance acting as a chelate complexing agent can preferably be contained in the passivation solution with a concentration in the range of 1-20 mmol/l. In addition to carboxylic acids (organic acids), other possible groups of chelating complexing agents are also: alcohols, phenols, naphthols, enols, thiols, sulfonic acid, phosphoric acid esters, phosphonic acid.

Die in der Passivierungslösung enthaltene Chelatkomplexbildner-Substanz (nachfolgend beispielhaft die Weinsäure) ermöglicht einen im Vergleich zum Stand der Technik einwandfreien Schichtbildungsmechanismus zur Bildung der Konversionsschicht: So wirkt in einem ersten Prozessschritt die Weinsäure als Chelatkomplexbildner, bei dem die in der Passivierungslösung koordinativ gebundenen Ca2+-Ionen im jeweiligen Weinsäure-Molekül komplexiert werden, und zwar unter Bildung eines Chelatkomplexes. Im Chelatkomplex sind die Ca2+-Ionen durch elektrostatische Anziehung an das Weinsäure-Molekül gebunden. Hintergrund ist, dass die freien Elektronenpaare bei den funktionellen C=O-Endgruppen der Weinsäure eine hohe Dichte negativer Ladungsträger erzeugen, die eine Wechselwirkung mit den positiv geladenen Ionen (Mg2+, Ca2+) eingehen. Der Chelatbildner (zum Beispiel Aminosäuren/Vitamine) kann somit Kationen binden. Wird anstelle der Weinsäure eine Aminosäure (zum Beispiel die Aminosäure L-Arginin) oder ein geeignetes Vitamin als Chelatkomplexbildner in der Passivierungslösung verwendet, sind die funktionellen Gruppen nicht C=O-Endgruppen, sondern NH2/NH-Endgruppen oder COOH-Endgruppen oder dergleichen.The chelate complexing substance contained in the passivation solution (tartaric acid as an example below) enables a flawless layer formation mechanism for the formation of the conversion layer compared to the prior art: In a first process step, the tartaric acid acts as a chelate complexing agent, in which the Ca 2 + ions are complexed in the respective tartaric acid molecule, with the formation of a chelate complex. In the chelate complex, the Ca 2+ ions are bound to the tartaric acid molecule by electrostatic attraction. The background is that the free pairs of electrons in the functional C=O end groups of tartaric acid create a high density of negative charge carriers, which interact with the positively charged ions (Mg 2+ , Ca 2+ ). The chelating agent (to Example amino acids/vitamins) can thus bind cations. If, instead of tartaric acid, an amino acid (for example the amino acid L-arginine) or a suitable vitamin is used as a chelating agent in the passivation solution, the functional groups are not C=O end groups, but rather NH 2 /NH end groups or COOH end groups or the like .

In einem zweiten Prozessschritt wird der Chelatkomplex über gegebenenfalls deprotonierte funktionelle Gruppen, das heißt zum Beispiel über OH-Endgruppen, an die metallische Bauteil-Oberfläche kurzzeitig physikalisch-reversibel adsorbiert. Die im Chelatkomplex gebundenen Ca2+-Ionen werden daher mit an die metallische Bauteil-Oberfläche transportiert. Dort kommt es zur Reaktion mit den in der Passivierungslösung gelösten Phosphaten und zur Bildung der kalziumphosphathaltigen Konversionsschicht. Anschließend erfolgt eine Desorption des Chelatkomplexbildners (das heißt des Chelatliganden) und der gleiche Prozess kann erneut stattfinden.In a second process step, the chelate complex is temporarily physically and reversibly adsorbed to the metallic component surface via any deprotonated functional groups, i.e. for example via OH end groups. The Ca 2+ ions bound in the chelate complex are therefore also transported to the metallic component surface. There it reacts with the phosphates dissolved in the passivation solution and forms the conversion layer containing calcium phosphate. Subsequently, the chelating agent (ie the chelating ligand) is desorbed and the same process can take place again.

Mittels der erfindungsgemäßen Passivierungslösung kann im Vergleich zum obigen Stand der Technik eine weitere Reduktion der Kontaktkorrosionsströme mit Aluminium, Stahl, Zink, Kohlenstofffasern oder CFK erfolgen. Ferner ergibt sich ein zusätzlicher Anstieg des Durchtrittswiderstands. Je höher der Durchtrittswiderstand der Konversionsschicht, desto geringer sind die Korrosionsströme. Der Durchtrittswiderstand verhält sich daher umgekehrt proportional zu den Korrosionsströmen. Darüber hinaus wird im Vergleich zum obigen Stand der Technik das passive Verhalten der Konversionsschicht gesteigert, und zwar aufgrund des im Wesentlichen geschlossenen, rissarmen Schichtaufbaus der Konversionsschicht.By means of the passivation solution according to the invention, a further reduction in contact corrosion currents with aluminum, steel, zinc, carbon fibers or CFRP can take place compared to the above prior art. Furthermore, there is an additional increase in the penetration resistance. The higher the penetration resistance of the conversion layer, the lower the corrosion currents. The penetration resistance is therefore inversely proportional to the corrosion currents. In addition, the passive behavior of the conversion layer is increased in comparison to the above prior art, due to the essentially closed, low-crack layer structure of the conversion layer.

Das mit der passivierten Oberfläche ausgebildete Metallbauteil kann branchenübergreifend eingesetzt werden. Beispielhaft kann das Metallbauteil im medizinischen Bereich angewendet werden. Alternativ ist das Metallbauteil gegebenenfalls im Automobilbereich einsetzbar, und zwar sichtgeschützt innerhalb des Fahrzeugs oder als nach außen sichtbares Außenteil. Beispielhaft kann das Metallbauteil als ein fahrzeuginnenseitiger Display-Rahmen, ein Aggregateteil, ein Fahrwerksteil oder ein Bestandteil einer Sitzrahmenstruktur realisiert sein.The metal component designed with the passivated surface can be used across all sectors. For example, the metal component can be used in the medical field. Alternatively, the metal component can optionally be used in the automotive sector, namely hidden from view inside the vehicle or as an external part that is visible from the outside. For example, the metal component can be implemented as a vehicle interior display frame, an assembly part, a chassis part or a component part of a seat frame structure.

Bei einem Bauteil-Werkstoff aus Aluminium ergibt sich mit der Passivierungslösung eine kompakte kalziumphosphat- und aluminiumhydroxid/oxidhaltige Beschichtung mit Aminosäuren. Die Schichtmorphologie ist dabei im Wesentlichen geschlossen, das heißt zumindest rissarm, ausgebildet. Alternativ dazu ergibt sich bei einem Bauteil-Werkstoff aus Magnesium eine kompakte kalziumphosphat- und magnesiumhydroxid/oxidhaltige Beschichtung, deren Schichtmorphologie ebenfalls im Wesentlichen geschlossen sowie rissarm ausgebildet ist.In the case of a component material made of aluminum, the passivation solution produces a compact coating containing calcium phosphate and aluminum hydroxide/oxide with amino acids. The layer morphology is essentially closed, that is to say at least with few cracks. As an alternative to this, a component material made of magnesium results in a compact coating containing calcium phosphate and magnesium hydroxide/oxide, the layer morphology of which is also essentially closed and has few cracks.

Die Passivierungslösung kann bevorzugt als Aktivatoren zur Aktivierung der Oberfläche des Bauteils zumindest die folgenden Bestandteile aufweisen:

  • NaCl mit einer Konzentration zwischen 5500 und 7500, insbesondere 6400 mg/l; und/oder
  • KCl mit einer Konzentration zwischen 300 und 500, insbesondere 400 mg/l.
The passivation solution can preferably have at least the following components as activators for activating the surface of the component:
  • NaCl with a concentration between 5500 and 7500, in particular 6400 mg/l; and or
  • KCl with a concentration between 300 and 500, in particular 400 mg/l.

Sowohl NaCl als auch KCl wirken als Chlorid-Quelle und unterstützen eine Aktivierung der Schichtbildung, bei der vermehrt Werkstoff-Ionen aus der Oberfläche des Bauteils herausgelöst werden, die für die Schichtbildung notwendig sind. Zudem enthält die Passivierungslösung MgSO4·7H2O mit einer Konzentration zwischen 100 und 400, insbesondere 200 mg/l.Both NaCl and KCl act as a chloride source and support activation of the layer formation, in which more material ions are released from the surface of the component, which are necessary for the layer formation are necessary. In addition, the passivation solution contains MgSO 4 .7H 2 O with a concentration of between 100 and 400, in particular 200 mg/l.

Zur Unterstützung der Schichtbildung sind zudem Ca2+- und/oder PO4 3--Ionen als Fragmente in der Konversionsschicht eingebaut. In diesem Fall kann die Passivierungsschicht Kalziumphosphate enthalten.Ca 2+ and/or PO 4 3- ions are also built into the conversion layer as fragments to support layer formation. In this case, the passivation layer can contain calcium phosphates.

Darüber hinaus weist die Konversionsschicht karbonathaltige Bestandteile auf. Zur Bereitstellung solcher karbonathaltigen Schichtbestandteile kann die Passivierungslösung NaHCO3 enthalten. Die Karbonatbildung ist zudem abhängig von gegebenenfalls zugeführtem CO2.In addition, the conversion layer has carbonate-containing components. To provide such carbonate-containing layer components, the passivation solution can contain NaHCO 3 . Carbonate formation is also dependent on any CO 2 that may have been added.

Die Passivierungslösung kann in einer besonders bevorzugten Ausführungsvariante zumindest genau die folgenden Bestandteile in Kombination enthalten: NaCl mit einer Konzentration zwischen 5000 und 8000, insbesondere 6400 mg/l; und/oder KCl mit einer Konzentration zwischen 300 und 500, insbesondere 400 mg/l, NaH2PO4 mit einer Konzentration zwischen 100 und 170, insbesondere 124 mg/l, und/oder CaCl2 mit einer Konzentration zwischen 170 und 300, insbesondere 200 mg/l NaHCO3 mit einer Konzentration zwischen 3500 und 4500, insbesondere 3700 mg/l MgSO4·7H2O mit einer Konzentration zwischen 100 und 400, insbesondere 200 mg/l Chelatkomplexbildner mit insbesondere 1 bis 20 mmol/l In a particularly preferred embodiment variant, the passivation solution can contain at least exactly the following components in combination: NaCl with a concentration between 5000 and 8000, in particular 6400 mg/l; and or KCl with a concentration between 300 and 500, in particular 400 mg/l, NaH2PO4 _ with a concentration between 100 and 170, in particular 124 mg/l, and/or CaCl 2 with a concentration between 170 and 300, in particular 200 mg/l NaHCO 3 with a concentration between 3500 and 4500, in particular 3700 mg/l MgSO4.7H2O _ with a concentration between 100 and 400, in particular 200 mg/l chelating agents with in particular 1 to 20 mmol/l

Die erfindungsgemäße Passivierungsreaktion kann bei einem pH-Wert von etwa 7 erfolgen. In diesem Fall läuft die Beschichtungsreaktion nur langsam ab. Alternativ kann die Beschichtungsreaktion auch im sauren Bereich stattfinden. Die Beschichtungsreaktion kann durch Erhöhung der Temperatur, Reduzierung des pH-Wertes und/oder durch Polarisation und/oder Erhöhung des Partialdruckes von CO2 beschleunigt werden. Der Beschichtungsprozess kann bevorzugt mit Hilfe einer pH-Wert-Reduktion (pH von 1 bis 5) und mit Hilfe einer Temperaturerhöhung von normaler Raumtemperatur um 15° bis 80°C beschleunigt werden.The passivation reaction according to the invention can take place at a pH of about 7. In this case, the coating reaction proceeds slowly. Alternatively, the coating reaction can also take place in the acidic range. The coating reaction can be accelerated by increasing the temperature, reducing the pH and/or by polarizing and/or increasing the partial pressure of CO 2 . The coating process can preferably be accelerated with the help of a pH value reduction (pH from 1 to 5) and with the help of a temperature increase from normal room temperature by 15° to 80°C.

In einem speziellen Anwendungsfall kann das Metallbauteil ein Fahrzeugteil sein, das zunächst mit der erfindungsgemäßen Passivierungslösung unter Bildung der Konversionsschicht vorbehandelt wird. Die Konversionsschicht des Bauteils kann in einem folgenden Beschichtungsprozess mit zumindest einer weiteren Schicht überdeckt werden.In a specific application, the metal component can be a vehicle part, which is first pretreated with the passivation solution according to the invention to form the conversion layer. The conversion layer of the component can be covered with at least one further layer in a subsequent coating process.

Beispielhaft weist der Beschichtungsprozess einen ersten Beschichtungsschritt auf, bei dem eine KTL-Schicht, das heißt eine organische Schutzschicht, gebildet wird. Dies erfolgt in einem Tauchverfahren (das heißt KTL) unter angelegter Gleichspannung, wodurch die im Tauchbad gelösten Lackpartikel vom Bauteil angezogen werden und dort unter Bildung der KTL-Schicht haften bleiben. In einem weiteren Beschichtungsschritt wird dann eine Pulverbeschichtung aufgebracht. Dies erfolgt in einem Pulverbeschichtungsprozess unter angelegter Gleichspannung. Im Hinblick auf eine prozesssichere Beschichtung ist die bereits oben erwähnte geschlossene, rissarme Schichtmorphologie von besonderer Bedeutung. Diese gewährleistet einerseits eine hohe Schutzwirkung der Konversionsschicht. Andererseits wird im Tauchverfahren und im Pulverbeschichtungsprozess eine ausreichende elektrische Restleitfähigkeit durch die Konversionsschicht hindurch gewährleistet.For example, the coating process has a first coating step, in which a KTL layer, ie an organic protective layer, is formed. This is done in a dipping process (i.e. KTL) with DC voltage applied, whereby the paint particles dissolved in the dipping bath are attracted to the component and adhere there, forming the KTL layer. A powder coating is then applied in a further coating step. This is done in a powder coating process under applied DC voltage. With regard to a process-reliable coating, the above-mentioned closed, low-crack layer morphology is of particular importance. On the one hand, this ensures a high protective effect of the conversion layer. On the other hand, sufficient residual electrical conductivity through the conversion layer is ensured in the dipping process and in the powder coating process.

Im Anschluss an den Bauteil-Beschichtungsprozess kann in einem möglichen Anwendungsfall das Metallbauteil, zum Beispiel als ein sichtseitiges Außenteil, in einem Fügevorgang an die noch nicht lackierte Rohbaukarosserie gefügt werden. Die Rohkarosserie wird dann zusammen mit dem daran montierten Leichtmetallbauteil einem herkömmlichen Karosserie-Lackierprozess unterworfen. Das heißt es erfolgt eine Grundierung der Rohkarosserie im Tauchverfahren. Darauffolgend wird die mit der Grundierung versehene Rohkarosserie zu einer weiteren Beschichtungsstation geführt, in der ein KTL-Prozess erfolgt. Dem KTL-Prozess ist ein Durchlaufofen nachgeschaltet, in dem bei hoher Temperatur ein Einbrennen der KTL-Schicht erfolgt. Anschließend wird in einer weiteren Beschichtungsstation ein herkömmlicher automobiler Lackaufbau aufgebracht, der in einem nachfolgenden Trocknungsschritt ebenfalls unter hoher Temperatur eingebrannt wird.In one possible application, after the component coating process, the metal component, for example as an outer part on the visible side, can be joined to the not yet painted body shell in a single joining process. The body-in-white, together with the light metal component mounted on it, is then subjected to a conventional body painting process. This means that the body shell is primed using the immersion method. The body shell provided with the primer is then taken to another coating station, in which a KTL process takes place. The KTL process is followed by a continuous furnace in which the KTL layer is burned in at high temperatures. A conventional automotive paint structure is then applied in a further coating station, which is also baked at high temperature in a subsequent drying step.

Im obigen Karosserie-Lackierprozess ist das an der Rohkarosserie montierte Metallbauteil bereits mit einem Schichtaufbau vorbeschichtet, und zwar mit der Konversionsschicht, der KTL-Schicht und der Pulverbeschichtung. Das Metallbauteil ist somit elektrisch isoliert, so dass die im Rohkarosserie-Lackierprozess elektrisch applizierte KTL-Schicht nicht mehr haften bleiben, während sich der herkömmliche automobile Lackaufbau ohne weiteres auf das bereits beschichtete Metallbauteil applizieren lässt.In the above body painting process, the metal component mounted on the body shell is already pre-coated with a layer structure, namely with the conversion layer, the KTL layer and the powder coating. The metal component is thus electrically insulated, so that the KTL layer electrically applied in the body-in-white painting process no longer sticks, while the conventional automotive paint structure can be applied easily to the metal component that has already been coated.

Die vorstehend erläuterten und/oder in den Unteransprüchen wiedergegebenen vorteilhaften Aus- und/oder Weiterbildungen der Erfindung können - außer zum Beispiel in den Fällen eindeutiger Abhängigkeiten oder unvereinbarer Alternativen - einzeln oder aber auch in beliebiger Kombination zur Anwendung kommen.The advantageous configurations and/or developments of the invention explained above and/or reproduced in the subclaims can be used individually or in any combination, except, for example, in cases of clear dependencies or incompatible alternatives.

Die Erfindung und ihre vorteilhaften Aus- und Weiterbildungen sowie deren Vorteile werden nachfolgend anhand von Zeichnungen näher erläutert.The invention and its advantageous training and developments and their advantages are explained in more detail below with reference to drawings.

Es zeigen:

Fig. 1a
den Schichtaufbau eines fertig lackierten Metallbauteils,
Fig. 1b und 1c
jeweils Ansichten, die den Schichtbildungsmechanismus zur Bildung einer Konversionsschicht veranschaulichen;
Fig. 2 bis 4
jeweils Ablaufpläne, die Beschichtungsprozesse zur Herstellung des in der Fig. 1 gezeigten Schichtaufbaus veranschaulichen; und
Fig. 5 bis 7
jeweils stark vergrößerte Teilschnittansichten, die den Beschichtungsprozess bis zum Auftragen der KTL-Schicht veranschaulichen.
Show it:
Fig. 1a
the layer structure of a finished painted metal component,
Figures 1b and 1c
each shows views illustrating the layer formation mechanism for forming a conversion layer;
Figures 2 to 4
each schedule, the coating processes for the production of in the 1 illustrate the layer structure shown; and
Figures 5 to 7
in each case greatly enlarged partial sectional views that illustrate the coating process up to the application of the KTL layer.

In der Fig. 1a ist in einer stark vergrößerten Teilschnittansicht beispielhaft der Schichtaufbau 1 einer Lackbeschichtung auf der Oberfläche 25 eines Karosserie-Bauteils 3 gezeigt. Beispielhaft ist hier das Karosserie-Bauteil 3 aus Leichtmetall gefertigt, etwa aus Aluminium, Magnesium oder einer Legierung davon. Demzufolge weist der Schichtaufbau 1 unmittelbar an der Werkstück-Oberfläche 25 des Leichtmetallbauteils 3 eine Konversionsschicht 5 auf, die zur Passivierung sowie zum Korrosionsschutz dient. Die Konversionsschicht 5 ist von einer KTL-Schicht 6 überzogen. Auf dieser ist eine Pulverbeschichtung 7 gebildet, auf der ein herkömmlicher automobiler, mehrschichtiger Lackaufbau 9 (in der Fig. 1a aus Gründen der Übersichtlichkeit einschichtig dargestellt) aufgetragen ist. Wie aus der Fig. 1a weiter hervorgeht, weist die Konversionsschicht 5 eine im Wesentlichen geschlossene, rissarme Schichtmorphologie auf. Die Konversionsschicht 5 ist zudem so ausgebildet, dass in einem später beschriebenen KTL-Beschichtungsprozess eine ausreichende Restleitfähigkeit zwischen einem KTL-Tauchbad und dem Leichtmetall-Werkstoff des Bauteils 3 bereitgestellt ist.In the Fig. 1a The layer structure 1 of a paint coating on the surface 25 of a body component 3 is shown as an example in a greatly enlarged partial sectional view. Here, for example, the body component 3 is made of light metal, for example aluminum, magnesium or an alloy thereof. Accordingly, the layer structure 1 has a conversion layer 5 directly on the workpiece surface 25 of the light metal component 3, which serves for passivation and corrosion protection. The conversion layer 5 is covered by a KTL layer 6 . A powder coating 7 is formed on this, on which a conventional automotive, multi-layer paint structure 9 (in Fig. 1a shown in one layer for reasons of clarity) is applied. How from the Fig. 1a further shows that the conversion layer 5 has a substantially closed layer morphology with few cracks. The conversion layer 5 is also formed in such a way that sufficient residual conductivity is provided between a KTL immersion bath and the light metal material of the component 3 in a KTL coating process, which will be described later.

Die Fig. 1, wie auch die weiteren Fig. 2 bis 7, sind im Hinblick auf ein einfacheres Verständnis der Erfindung angefertigt. Von daher sind die Figuren lediglich grob vereinfachte Darstellungen, die keinen realitätsgetreuen Schichtaufbau 1 wiedergeben. So weist die Konversionsschicht 5 tatsächlich eine Schichtdicke auf, die im µm-Bereich liegt.the 1 , as well as the others Figures 2 to 7 , are prepared for easier understanding of the invention. Therefore, the figures are only roughly simplified representations that do not represent a realistic layer structure 1. Thus, the conversion layer 5 actually has a layer thickness that is in the μm range.

Nachfolgend wird anhand des in den Fig. 2 bis 4 gezeigten Ablaufplans ein in einer Lackieranlage durchgeführter Serienlackprozess beschrieben, in dem eine erfindungsgemäße Passivierungslösung Anwendung findet: Demzufolge erfolgen in der Fig. 2 als Vorbehandlungsschritte zunächst eine (optionale) mechanische Bearbeitung, zum Beispiel ein Schleifen. Anschließend wird eine naßchemische Vorbehandlung, das heißt ein Entfetten und ein Beizen, durchgeführt. Darauf folgt ein Passivierungsschritt, bei dem das Metallbauteil 3 zum Beispiel in ein Tauchbad aus der Passivierungslösung eingetaucht wird.The following is based on in the Figures 2 to 4 Shown flow chart describes a carried out in a paint shop series paint process in which a passivation solution according to the invention is used 2 as a pre-treatment step, an (optional) mechanical processing, for example grinding. A wet-chemical pre-treatment, ie degreasing and pickling, is then carried out. This is followed by a passivation step, in which the metal component 3 is immersed, for example, in an immersion bath made of the passivation solution.

Die Passivierungslösung enthält zumindest die folgenden Hauptbestandteile: NaCl mit 6400 mg/l KCl mit 400 mg/l NaH2PO4 mit 124 mg/l CaCl2 mit 200 mg/l NaHCO3 mit 3700 mg/l MgSO4·7H2O mit 200 mg/l Chelatligand zwischen 1 und 20 mmol/l The passivation solution contains at least the following main components: NaCl with 6400 mg/l KCl with 400 mg/l NaH2PO4 _ with 124 mg/l CaCl 2 with 200 mg/l NaHCO 3 with 3700 mg/l MgSO4.7H2O _ with 200 mg/l chelating ligand between 1 and 20 mmol/l

Dabei dient NaCl und KCl in der Passivierungslösung zur Aktivierung der Metall-Oberfläche 25. Die Komponenten NaH2PO4 und CaCl2 unterstützen den Beschichtungsprozess durch Einbau der Ca2+- und PO4 3--Ionen in die Konversionsschicht 5.NaCl and KCl in the passivation solution are used to activate the metal surface 25. The components NaH 2 PO 4 and CaCl 2 support the coating process by incorporating the Ca 2+ and PO 4 3- ions into the conversion layer 5.

Die Weinsäure bewirkt den nachfolgend anhand der Fig. 1b und 1c beschriebenen Schichtbildungsmechanismus zur Bildung der Konversionsschicht 5. So funktioniert die Weinsäure in einem ersten Prozessschritt (Fig. 1b) als ein sogenannter Chelatkomplexbildner, bei dem die in der Passivierungslösung koordinativ gebundenen Ca2+-Ionen im jeweiligen Weinsäure-Molekül komplexiert gebunden werden, und zwar unter Bildung eines Chelatkomplexes 8 (Fig. 1b). Im Chelatkomplex 8 sind die Ca2+-Ionen durch elektrostatische Anziehung (in der Fig. 1b und 1c durch gestrichelte Linien angedeutet) gebunden. Hintergrund ist, dass die freien Elektronenpaare bei den funktionellen C=O-Endgruppen sowie den OH-Endgruppen der Weinsäure eine hohe Dichte negativer Ladungsträger erzeugen, die eine Wechselwirkung mit den positiv geladenen Ionen (Mg2+, Ca2+) eingehen; der Chelatkomplexbildner (alternativ zur Weinsäure zum Beispiel auch Aminosäuren/Vitamine) kann somit Ionen binden. Wird anstelle der Weinsäure eine Aminosäure (zum Beispiel die Aminosäure L-Arginin) oder ein geeignetes Vitamin als Chelatkomplexbildner in der Passivierungslösung verwendet, sind die gegebenenfalls deprotonierten funktionellen Gruppen nicht C=O-Endgruppen, sondern NH2/NH-Endgruppen, COOH-Endgruppen, PO4 3--Endgruppen, SH-Endgruppen oder OH-Endgruppen.The tartaric acid causes the following based on the Figures 1b and 1c described layer formation mechanism for the formation of the conversion layer 5. This is how the tartaric acid works in a first process step ( Fig. 1b ) as a so-called chelate complexing agent, in which the Ca 2+ ions coordinated in the passivation solution are complexed in the respective tartaric acid molecule, forming a chelate complex 8 ( Fig. 1b ). In the chelate complex 8, the Ca 2+ ions are attracted by electrostatic attraction (in the Figures 1b and 1c indicated by dashed lines). The background is that the free pairs of electrons in the functional C=O end groups and the OH end groups of tartaric acid produce a high density of negative charge carriers, which interact with the positively charged ions (Mg 2+ , Ca 2+ ); the chelate complexing agent (alternative to tartaric acid, for example also amino acids/vitamins) can thus bind ions. If, instead of tartaric acid, an amino acid (for example the amino acid L-arginine) or a suitable vitamin is used as a chelating agent in the passivation solution, the possibly deprotonated functional groups are not C=O end groups, but rather NH 2 /NH end groups, COOH end groups , PO 4 3- end groups, SH end groups or OH end groups.

In einem zweiten Prozessschritt (Fig. 1c) wird der Chelatkomplex 8 über funktionelle Gruppen, das heißt beispielsweise über OH-Endgruppen, an die Oberfläche 25 des Metallbauteils 3 kurzzeitig physikalisch-reversibel adsorbiert (in der Fig. 1c mit Einfach-Pfeil angedeutet). Die im Chelatkomplex 8 gebundenen Ca2+-Ionen werden daher mit an die Oberfläche 25 transportiert. Dort kommt es zur Reaktion mit den in der Passivierungslösung gelösten Phosphaten (in der Fig. 1c mit einem Doppelpfeil angedeutet) und zur Bildung der kalziumphosphathaltigen Konversionsschicht 5. Anschließend erfolgt eine Desorption des Chelatkomplexbildners (das heißt des Chelatliganden) und der gleiche Prozess kann erneut stattfinden. Erfindungsgemäß ist die Weinsäure (oder auch eine andere geeignete Substanz) bevorzugt als alleiniger Chelatkomplexbildner in der Passivierungslösung enthalten. Auf diese Weise erfolgt ein dirigiertes Schichtwachstum, bei dem bevorzugt einzig die Weinsäure als Chelatkomplexbildner-Substanz wirkt. Der von der Weinsäure eingeleitete Schichtbildungsmechanismus ist daher nicht durch andere konkurrierende Substanzen beeinträchtigt, die ebenfalls als Chelatkomplexbildner wirken können. Auf diese Weise kann die Konversionsschicht 5 mit einer bevorzugt geschlossenen, rissarmen Schichtmorphologie ausgebildet werden. Die Konversionsschicht 5 weist daher im Vergleich zu Konversionsschichten mit Rissstrukturen eine verbesserte Schutzwirkung auf.In a second process step ( 1c ) The chelate complex 8 is attached via functional groups, that is, for example via OH end groups, to the Surface 25 of the metal component 3 is briefly physically and reversibly adsorbed (in the 1c indicated by a single arrow). The Ca 2+ ions bound in the chelate complex 8 are therefore also transported to the surface 25 . There, a reaction occurs with the phosphates dissolved in the passivation solution (in the 1c indicated by a double arrow) and to form the conversion layer 5 containing calcium phosphate. Subsequently, the chelate complexing agent (ie the chelate ligand) is desorbed and the same process can take place again. According to the invention, the tartaric acid (or another suitable substance) is preferably contained in the passivation solution as the sole chelate complexing agent. In this way, a directed layer growth takes place, in which preferably only the tartaric acid acts as a chelating substance. The stratification mechanism initiated by the tartaric acid is therefore not affected by other competing substances that can also act as chelating complexing agents. In this way, the conversion layer 5 can be formed with a preferably closed, low-crack layer morphology. The conversion layer 5 therefore has an improved protective effect compared to conversion layers with crack structures.

Wie oben erwähnt, wird im vorliegenden Ausführungsbeispiel als einzige Chelatkomplexbildner-Substanz Weinsäure verwendet. Es ist jedoch hervorzuheben, dass die Erfindung nicht auf dieses Ausführungsbeispiel beschränkt ist.As mentioned above, in the present embodiment, tartaric acid is used as the sole chelating agent. However, it should be emphasized that the invention is not limited to this exemplary embodiment.

Die erfindungsgemäße Konversionsschicht 5 weist zudem karbonathaltige Schichtbestandteile auf. Diese werden in der Passivierungslösung durch die Komponente NaHCO3 und CO2 (aus der Atmosphäre) bereitgestellt.The conversion layer 5 according to the invention also has carbonate-containing layer components. These are provided in the passivation solution by the components NaHCO 3 and CO 2 (from the atmosphere).

Insgesamt handelt es sich daher bei der erfindungsgemäßen Passivierungslösung um eine wässrige Behandlungsflüssigkeit, deren pH-Wert im Bereich von etwa 7 oder im sauren Bereich liegt. Die Passivierung erfolgt bevorzugt in dem Tauchbad bei Raumtemperatur. Die Behandlungszeit richtet sich nach dem eingestellten pH-Wert, der Prozesstemperatur und gegebenenfalls einer zusätzlichen Polarisation sowie der geforderten Solldicke der Beschichtung. Nach der Passivierung wird das Bauteil 3 einem Spül-/Trocknungsvorgang zugeführt. Der obige Beschichtungsprozess kann mittels einer pH-Wert-Reduktion auf einen pH-Wert von 1 bis 5 und/oder durch eine Temperaturerhöhung um 15 bis 80 °C beschleunigt werden.Overall, the passivation solution according to the invention is therefore an aqueous treatment liquid whose pH is in the range of about 7 or in the acidic range. The passivation preferably takes place in the immersion bath at room temperature. The treatment time depends on the set pH value, the process temperature and, if necessary, an additional polarization as well as the required nominal thickness of the coating. After the passivation, the component 3 is fed to a rinsing/drying process. The above coating process can be accelerated by reducing the pH to a value of 1 to 5 and/or by increasing the temperature by 15 to 80°C.

Das mit der Konversionsschicht 5 beschichtete Bauteil 3 wird im vorliegenden Anwendungsfall in der weiteren Prozeßabfolge (gemäß der Fig. 3) in einer Beschichtungsstation 17 mit einer KTL-Schicht 6 (das heißt einer organischen Schutzschicht) versehen. So erfolgt die KTL-Beschichtung in gängiger Praxis im Tauchverfahren, bei dem zwischen der Karosserie 15 und dem Tauchbecken eine elektrische Gleichspannung angelegt wird, wodurch die im Tauchbad gelösten Lackpartikel vom Bauteil 3 angezogen werden und dort gleichmäßig haften bleiben. Zusätzlich erforderliche Vor- oder Nachbehandlungsschritte sind aus Gründen des einfacheren Verständnisses der Erfindung weggelassen.The component 3 coated with the conversion layer 5 is in the present application in the further process sequence (according to the 3 ) in a coating station 17 with a KTL layer 6 (ie an organic protective layer). In common practice, KTL coating is carried out using the immersion method, in which an electrical DC voltage is applied between the body 15 and the immersion bath, as a result of which the paint particles dissolved in the immersion bath are attracted to the component 3 and adhere uniformly there. Additionally required pre- or post-treatment steps are omitted for the sake of easier understanding of the invention.

In einer nachgeschalteten Trocknungsstation 18 durchläuft das Bauteil 3 mit vorgegebener Fördergeschwindigkeit einen Durchlaufofen, in dem die KTL-Schicht 6 bei Prozesstemperaturen im Bereich von zum Beispiel 180°C eingebrannt wird. Anschließend wird im Prozessschritt II in einer Beschichtungsstation 20 eine Pulverbeschichtung durchgeführt, bei der die Schicht 7 (Fig. 1) auf das Bauteil 3 aufgetragen wird. Bei der Pulverbeschichtung 20 werden die Lackpartikel durch ein elektrostatisches Feld von unter Spannung stehenden Spitzköpfen zu dem geerdeten Bauteil 3 transportiert. Im Anschluss daran erfolgt in einer weiteren Station 19 ein Einbrennvorgang in einem Durchlaufofen.In a downstream drying station 18, the component 3 runs through a continuous furnace at a predetermined conveying speed, in which the KTL layer 6 is baked at process temperatures in the range of 180° C., for example. Then, in process step II, a powder coating is carried out in a coating station 20, in which the layer 7 ( 1 ) is applied to component 3. In the Powder coating 20, the paint particles are transported to the grounded component 3 by an electrostatic field from live spike heads. This is followed by a baking process in a continuous furnace in a further station 19 .

Im Anschluss an den Bauteil-Beschichtungsprozess L (das heißt Prozessschritte I und II der Fig. 3) wird das Leichtmetallbauteil 3 in einem beispielhaft möglichen Anwendungsfall als ein sichtseitiges Fahrzeug-Außenteil in einem Fügevorgang (zum Beispiel Kleben und/oder Schrauben) an eine noch nicht lackierte Rohbaukarosserie 15 gefügt. Die Rohkarosserie 15 wird in einem kontinuierlichen Prozess in eine Karosserie-Lackieranlage (siehe Fig. 4) gefördert. Dort erfolgt eine Grundierung 25 im Tauchverfahren. Darauffolgend wird die mit der Grundierung versehene Rohkarosserie 15 zu einer weiteren Beschichtungsstation 29 geführt, in der ein KTL-Prozess erfolgt. Dem KTL-Prozess 29 ist ebenfalls ein Durchlaufofen 31 nachgeschaltet, in dem bei hoher Temperatur ein Einbrennen der Beschichtung erfolgt. Anschließend wird in einer weiteren Beschichtungsstation 33 ein herkömmlicher automobiler Vierschicht-Lackaufbau 9 aufgebracht, der nachfolgend einem Einbrennvorgang 35 unterworfen wird.Following the component coating process L (i.e. process steps I and II of 3 ) In an exemplary possible application, the light metal component 3 is joined as a visible-side vehicle exterior part in a joining process (for example gluing and/or screwing) to a body shell 15 that has not yet been painted. The body shell 15 is in a continuous process in a body painting plant (see 4 ) promoted. There is a primer 25 in the immersion process. The body shell 15 provided with the primer is then fed to a further coating station 29 in which a KTL process takes place. The KTL process 29 is also followed by a continuous furnace 31 in which the coating is baked at high temperature. Then, in a further coating station 33, a conventional automotive four-layer paint structure 9 is applied, which is then subjected to a baking process 35.

Der in der Fig. 4 gezeigte Karosserie-Lackierprozess wird mit bereits vorbeschichtetem Leichtmetallbauteil 3 durchgeführt. Das heißt das Leichtmetallbauteil 3 ist elektrisch isoliert, so dass die im Rohkarosserie-Lackierprozess applizierte KTL-Schicht nicht mehr haften bleiben, wogegen sich der herkömmliche automobile Lackaufbau 9 (das heißt ein Vierschichtaufbau) ohne weiteres auf der Pulverbeschichtung 7 des Metallbauteils 3 applizieren lässt.The Indian 4 The body painting process shown is carried out with a light metal component 3 that has already been precoated. This means that the light metal component 3 is electrically insulated, so that the KTL layer applied in the body-in-white painting process no longer sticks, whereas the conventional automotive paint structure 9 (i.e. a four-layer structure) can easily be applied to the powder coating 7 of the metal component 3.

In den Fig. 5 bis 7 ist in Ansichten entsprechend der Fig. 1 das Leichtmetallbauteil 3 in unterschiedlichen Prozessschritten gezeigt. So ist in der Fig. 5 das Leichtmetallbauteil 3 mit gereinigter sowie freigelegter metallischer Oberfläche 25 gezeigt. In der Fig. 6 ist das Leichtmetallbauteil 3 nach erfolgter Passivierung sowie Spülen oder Trocknen gezeigt. Demzufolge ist die Konversionsschicht 5 auf der Oberfläche 25 des Leichtmetallbauteils appliziert. In der Fig. 7 ist das Leichtmetallbauteil 3 nach erfolgtem KTL-Prozess gezeigt.In the Figures 5 to 7 is in views according to the 1 the light metal component 3 is shown in different process steps. So is in the figure 5 the light metal component 3 is shown with a cleaned and exposed metallic surface 25 . In the 6 the light metal component 3 is shown after passivation and rinsing or drying has taken place. Accordingly, the conversion layer 5 is applied to the surface 25 of the light metal component. In the 7 the light metal component 3 is shown after the KTL process has taken place.

Es ist hervorzuheben, dass die Erfindung keinesfalls auf diesen obigen speziellen Anwendungsfall beschränkt ist. Vielmehr kann in anderen Anwendungsfällen die Konversionsschicht 5 auch als alleinige Schicht (das heißt im Einschichtaufbau ohne zusätzliche Zwischen- und Deckschichten) auf dem Leichtmetallbauteil 3 verbleiben.It should be emphasized that the invention is in no way limited to the above specific application. Rather, in other applications, the conversion layer 5 can also remain on the light metal component 3 as the sole layer (ie in a single-layer structure without additional intermediate and cover layers).

Claims (10)

  1. Passivating solution for forming a conversion layer (5) for a surface (25) of a metal component (3) in a method for passivating the surface (25) of the metal component (3), in which a calcium phosphate containing conversion layer (5) is produced on the surface (25) in in a passivating step using the aqueous passivating solution, which comprises oxides, hydroxides and carbonates of the component material and of the passivating solution, wherein the passivating solution for forming the conversion layer (5) comprises a substance acting as chelate complexing agent, wherein the conversion layer (5) of the component (3) is covered by at least one layer (6, 7, 9) in a subsequent coating process (L), and wherein the coating process (L) comprises a first coating step (I), in which an organic protective layer (6) is formed, and indeed in a dipping method under applied DC voltage, whereby the paint particles dissolved in the dipping bath are attracted to the component (3) and adhere there forming the protective layer (6), wherein the pH value of the passivating solution is in a neutral to acid range, and wherein the layer morphology during the first coating step (I) ensures a sufficient residual electrical conductivity between the dipping bath and the component material, characterised in that, for the building up of the conversion layer (5) with a closed layer morphology having few cracks, the passivating solution comprises exactly one substance acting as a chelate complexing agent and the passivating solution contains MgSO4·7H2O at a concentration between 100 and 400, in particular 200 mg/l.
  2. Passivating solution according to claim 1, characterised in that an organic substance, optionally with deprotonated functional groups with one or more free electron pairs, is used as chelate complexing agent, i.e. for example OH end groups, COOH end groups, NH2 end groups and the like, and that, in particular, an organic acid or the salts thereof, an amino acid or a suitable vitamin is used as organic substance, and/or that, additionally or alternatively, the following substances can be used as chelate complexing agent: alcohols, phenols, naphthols, enols, thiols, sulfonic acid, phosphoric acid ester, phosphoric acid.
  3. Passivating solution according to claim 2, characterised in that the organic acid contained in the passivating solution is tartaric acid, acetic acid or L-arginine.
  4. Passivating solution according to any of the preceding claims, characterised in that the substance acting as chelate complexing agent is contained in the passivating solution at a concentration in the range 1-20 mmol/l.
  5. Passivating solution according to any of the preceding claims, characterised in that at least the surface (25) of the component (3) is formed by a light metal, in particular magnesium, aluminium or the alloys thereof.
  6. Passivating solution according to any of the preceding claims, characterised in that the passivating solution comprises at least the following constituents as activators for activating the surface (25) of the component (3):
    NaCl at a concentration between 5000 and 8000, in particular 6400 mg/l; and/or
    KCl at a concentration between 300 and 500, in particular 400 mg/l,
    and that, in particular, the components NaCl and KCl are contained in combination in the passivating solution.
  7. Passivating solution according to any of the preceding claims, characterised in that the passivating solution contains the following constituents to support the layer formation, which are integrated as fragments (i.e. Ca2+ or PO4 3-) in the conversion layer (5):
    NaH2PO4 at a concentration between 100 and 170, in particular 124 mg/l, and/or
    CaCl2 at a concentration between 170 and 300, in particular 200 mg/l.
  8. Passivating solution according to any of the preceding claims, characterised in that the conversion layer (5) for supporting the layer formation comprises carbon-containing constituents, and that, in particular, the passivating solution contains NaHCO3 for providing the carbon-containing constituents, in particular at a concentration between 3500 and 4500, in particular 3700 mg/l.
  9. Passivating solution according to any of the preceding claims, characterised in that the aqueous passivating solution contains at least exactly the following constituents in combination:
    NaCl at a concentration between 5000 and 8000, in particular 6400 mg/l; and/or
    KCl at a concentration between 300 and 500, in particular 400 mg/l,
    NaH2PO4 at a concentration between 100 and 170, in particular 124 mg/l, and/or
    CaCl2 at a concentration between 170 and 300, in particular 200 mg/l
    NaHCO3 the concentration between 3500 and 4500, in particular 3700 mg/l
    MgSO4·7H2O at a concentration between 100 and 400, in particular 200 mg/l chelate complexing agent with, in particular, 1 to 20 mmol/l.
  10. Passivating solution according to any of the preceding claims, characterised in that the coating process (L) comprises at least one further coating step (II), in which at least one layer (7) is applied, in particular in a powder coating process under applied DC voltage.
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