EP2255026B1 - Optimized passivation on ti-/zr-basis for metal surfaces - Google Patents

Description

The present invention relates to a chromium-free aqueous agent based on water-soluble compounds of titanium and / or zirconium and a process for the corrosion-protective conversion treatment of metallic surfaces. The chromium-free aqueous agent is suitable for treating various metallic materials joined together in composite structures, including steel or galvanized or alloy-galvanized steel, and any combination of these materials. Furthermore, surfaces of aluminum and its alloys can be treated with the agent according to the invention to protect against corrosion. The corrosion protection treatment is intended above all as a pretreatment for a subsequent dip coating.

The invention further comprises a metallic substrate, which has been treated according to a predetermined sequence of processes with the chromium-free agent according to the invention, and its use, in particular in the automotive production of bodies.

Anticorrosion agents, which are an acidic aqueous solution of fluoro complexes, have long been known. They are increasingly used as a replacement for chromating, which are increasingly less used because of the toxicological properties of chromium compounds. As a rule, such solutions of fluoro-complexes contain further anti-corrosive agents that further improve the anti-corrosion effect and paint adhesion.

For example, this describes DE-A-19 33 013 in one embodiment, a treating solution which is an aqueous solution of ammonium hexafluorozirconate, sodium nitrate, cobalt nitrate and sodium m-nitrobenzenesulfonate and a pH of 5.2. The solution can be used to treat zinc, steel or aluminum surfaces. EP-A-1 571 237 describes a treatment solution and treatment method for iron, zinc, aluminum and magnesium containing surfaces. This solution has a pH in the range of 2 to 6 and contains 5 to 5000 ppm of zirconium and / or titanium and 0.1 to 100 ppm of free fluoride. In addition, the solution may contain further components selected from chlorate, bromate, nitrite, nitrate, permanganate, vanadate, hydrogen peroxide, tungstate, molybdate or in each case the associated acids. Organic polymers may also be present. After treatment with such a solution, the metal surfaces can be rinsed with another passivating solution.

The WO 93/05198 describes a "dry-in-place" process in which chromium-free compositions containing as one component fluorocomplexes of titanium, zirconium, hafnium, silicon and boron and as a second component cations of elements selected from cobalt, magnesium, titanium, zinc, nickel, tin , Zirconium, iron, aluminum and copper, both components must be in a certain minimum ratio to one another, in particular be applied to galvanized steel surfaces. In the exemplary embodiments, the advantageous effect of compositions containing compounds of cobalt or magnesium as the second component is documented.

From the WO 07/065645 are also aqueous compositions that contain fluorocomplexes of, inter alia, titanium and / or zirconium, wherein in addition a further component is included, which is selected from: nitrate ions, copper ions, silver ions, vanadium or vanadate ions , Bismuth ions, magnesium ions, zinc ions, manganese ions, cobalt ions, nickel ions, tin ions, buffer systems for the pH range from 2.5 to 5.5, aromatic carboxylic acids having at least two groups containing donor atoms, or derivatives of such carboxylic acids, silica particles having a mean particle size below 1 micron. The WO 07/065645 further teaches that for the suppression of excess free fluoride aluminum ions as "Fluoride scavengers" can be added, but without specifying what characterizes an excess of free fluoride and under what conditions aluminum ions can be used as a "fluoride scavenger".

The EP 1405933 discloses a composition for the treatment of surfaces of iron and / or zinc containing at least one metal from the group Ti, Zr, Hf and Si and a fluorine ion source, wherein as a condition of the concentration ratios of these two components is provided that the amount of free Fluoride ions does not exceed 500 ppm. As the "fluoride scavenger", compounds containing the elements silver, aluminum, copper, iron, manganese, magnesium, nickel, cobalt and zinc are named.

The object of the present invention is now to provide an aqueous chromium-free, titanium and / or zirconium-based agent for the conversion treatment of metallic surfaces which, for high fluoride contents of the composition, further optimally passivates the treated metal surface so that the directly treated metallic component on the one hand, a sufficient temporary protection against corrosion is imparted and on the other hand, in cooperation with an organic primer coating or an organic dip paint the high demands on a permanent corrosion protection are met, with an extremely good paint adhesion is guaranteed.

High fluoride contents according to the task are then present in the aqueous medium, if the total number of fluorine atoms is greater than the number of maximum complexable by the elements of titanium and / or zirconium fluorine atoms, ie if the molar ratio of the total Fluorine atoms to the total number of titanium and / or zirconium atoms exceeds 6.

1. (A) ein oder mehrere wasserlösliche Verbindungen enthaltend zumindest ein Atom ausgewählt aus den Elementen Titan und/oder Zirkon, wobei die Gesamtkonzentration an diesen Elementen 2,5·10^-4 mol/l nicht unterschreitet, aber nicht größer als 2,0·10^-2 mol/l ist.
2. (B) ein oder mehrere wasserlösliche Verbindungen als Quelle für Fluorid-Ionen enthaltend zumindest ein Fluor-Atom,

wobei das Mittel die benannten Elemente der jeweiligen Komponenten (A) und (B) in einem molaren Verhältnis A : B von 1 : z enthält, wobei z eine reelle Zahl R und größer als 6 ist {z ∈ R| z > 6}, dadurch gekennzeichnet, dass im Mittel zusätzlich

• (C) ein oder mehrere wasserlösliche Verbindungen, die Kupfer-Ionen freisetzen, enthaltend zumindest ein Kupfer-Atom, sowie
• (D) ein oder mehrere wasserlösliche und/oder wasserdispergierbare Verbindungen, die Metall-Ionen freisetzen, aber keine Quelle für FluoridIonen sind, enthaltend zumindest ein Metall-Atom ausgewählt aus der Gruppe bestehend aus Kalzium, Magnesium, Aluminium, Bor, Zink, Eisen, Mangan und/oder Wolfram enthalten sind, wobei das molare Verhältnis D : B der Gesamtzahl der Metall Atome der Komponente (D) zur Gesamtzahl der Fluor-Atome der Komponente (B) nicht kleiner als $\frac{z-6}{4z}$
  
  ist.

wobei sich Komponente (D) zumindest aus wasserlöslichen und/oder wasserdispergierbaren Verbindungen, die Aluminium-Ionen enthalten Zusammensetz, und das molare Verhältnis D : B der Gesamtzahl an Aluminium-Atomen der Komponente (D) zur Gesamtzahl an Fluor-Atomen der Komponente (B) vorzugsweise nicht größer als $\frac{z-6}{z}$

ist.The problem underlying the invention is solved by an aqueous chromium-free agent suitable for the conversion treatment of metallic surfaces containing

1. (A) one or more water-soluble compounds containing at least one atom selected from the elements titanium and / or zirconium, wherein the total concentration of these elements not less than 2.5 x 10 ^-4 mol / l, but not greater than 2.0 x 10 ^-2 mol / l.
2. (B) one or more water-soluble compounds as a source of fluoride ions containing at least one fluorine atom,

wherein the agent contains the named elements of the respective components (A) and (B) in a molar ratio A: B of 1: z, where z is a real number R and greater than 6 {z ∈ R | z> 6}, characterized in that in addition on average

• (C) one or more water-soluble compounds which release copper ions containing at least one copper atom, and
• (D) one or more water-soluble and / or water-dispersible compounds which release metal ions but are not sources of fluoride ions containing at least one metal atom selected from the group consisting of calcium, magnesium, aluminum, boron, zinc, iron, Manganese and / or tungsten wherein the molar ratio D: B of the total number of metal atoms of component (D) to the total number of fluorine atoms of component (B) is not less than $\frac{z-6}{4z}$
  
  is.

wherein component (D) is composed of at least water-soluble and / or water-dispersible compounds containing aluminum ions, and the molar ratio D: B of the total number of aluminum atoms of component (D) to the total number of fluorine atoms of component (B ) preferably not larger than $\frac{z-6}{z}$

is.

wird erreicht, dass eine ausreichende Menge an "Fluorid-Fängern" im erfindungsgemäßen Mittel enthalten ist, um nach dem In-Kontakt-Bringen des Mittels mit einer Eisenoberfläche, vorzugsweise mit einer unlegierten Stahloberfläche, bei einer Behandlungsdauer von 90 s und einer Behandlungstemperatur von 30°C auf dieser eine Schichtauflage von zumindest 20 mg/m² bezogen auf die Elemente der Komponente (A) ausgewählt aus Titan und/oder Zirkon zu bewirken.By maintaining this specific molar ratio D: B of the total number of metal atoms of component (D) to the total number of fluorine atoms of component (B) of at least $\frac{z-6}{4z}$

it is achieved that a sufficient amount of "fluoride scavengers" is included in the composition according to the invention, after contacting the agent with an iron surface, preferably with an unalloyed steel surface, at a treatment time of 90 s and a treatment temperature of 30 ° C on this one layer of at least 20 mg / m ² based on the elements of component (A) selected from titanium and / or zirconium effect.

nicht unterschreiten, erzeugen insbesondere bei ihrer Anwendung im Tauchverfahren eine hinreichend passivierende Konversion der Metalloberflächen.Compositions according to the invention which have this concrete molar ratio D: B of $\frac{z-6}{4z}$

do not fall below, produce a sufficiently passivating conversion of the metal surfaces, especially when used in the dipping process.

The minimum concentration according to the invention of the elements titanium and / or zirconium of the components (A) represents a threshold value with regard to the conversion layer formation and must therefore be present in the aqueous medium. If the concentration is below this value, there is no homogeneous conversion of the metallic surface to form a mixed oxydic-hydroxidic zirconium-containing passive layer and the layer supports based on the elements titanium and / or zirconium are significantly below 20 mg / m ² . In such a case, the deposition of copper dominates, while the passivating surface layer formation almost completely disappears.

On the other hand, concentrations of the elements titanium and / or zirconium according to the components (A) of more than 2.0 × 10 ^-2 mol / l in the aqueous medium are not economical and, in addition, do not give any additional advantages in the treatment of metallic components of corrosion protection. Rather, such high concentrations complicate the processability and increase the operating costs of the conversion baths due to inevitably incurred additional regeneration and reprocessing measures.

Particularly preferred are those aqueous chromium-free compositions whose component (A) consists exclusively of water-soluble compounds of zirconium.

kann daher auch als Richtwert angesehen werden für eine erfindungsgemäße Zusammensetzung, die unabhängig von der speziellen Verfahrensweise beim In-Kontakt-Bringen der Zusammensetzung eine hinreichende passivierende Konversion der Metalloberfläche bewirkt, wobei für eine solche hinreichende Konversion zusätzlich die Bedingung erfüllt sein muss, dass der Quotient D : B keine Werte unterschreitet für die nach dem In-Kontakt-Bringen des Mittels mit einer Eisenoberfläche, vorzugsweise mit einer unlegierten Stahloberfläche, bei einer Behandlungsdauer von 90 s und einer Behandlungstemperatur von 30°C auf dieser eine Schichtauflage von weniger als 20 mg/m² bezogen auf die Elemente der Komponente (A) ausgewählt aus Titan und/oder Zirkon erzielt wird.The quotient D: B of at least $\frac{z-6}{4z}$

can therefore also be regarded as a guideline for a composition according to the invention which, regardless of the special procedure when contacting the composition causes a sufficient passivating conversion of the metal surface, wherein for such a sufficient conversion additionally the condition must be satisfied that the quotient D: B does not fall below a value of less than 20 mg on the layer after contact of the agent with an iron surface, preferably with an unalloyed steel surface, for a treatment time of 90 s and a treatment temperature of 30 ° C. m ^{2 is} obtained based on the elements of component (A) selected from titanium and / or zirconium.

vorzugsweise nicht kleiner als $\frac{z-6}{2z}$

ist.In particular, it has been found that such aqueous agents are advantageous for conversion layer formation in which the molar ratio D: B of the total number of metal atoms of component (D) to the total number of fluorine atoms of component (B) is not less than $\frac{z-6}{3z}.$

preferably not less than $\frac{z-6}{2z}$

is.

The advantageous effect consists in the displacement of the composition of the conversion layer after treatment of a metallic surface with the agent according to the invention in favor of higher layer supports with respect to the elements titanium and / or zirconium, in particular relative to the layer of copper, so that increased corrosion protection and improved adhesion properties applied to subsequently organic topcoats are the result.

The chromium-free and titanium and / or zirconium-based agent is preferably used according to the invention when the molar ratio D: B does not exceed values for which, after contacting the agent with an iron surface, preferably with a carbon steel surface at a treatment time of 90 s and a treatment temperature of 30 ° C on this a layer of less than 20 mg / m ² based on the elements the component (A) selected from titanium and / or zirconium results. It could be shown in this context that closed homogeneous conversion layers are formed only at layer supports of the elements titanium and / or zirconium of about 20 mg / m ² . In the case of insufficient conversion of the metal surface, in the presence of the copper ions in the aqueous chromium-free medium, the electroless deposition of metallic copper predominates. However, a dominant metallic coating layer is not suitable to build up a sufficient corrosion protection and in particular to impart sufficient adhesion to organic surface layers. Optimum results with respect to the corrosion protection are achieved by means according to the invention when they bring about a complete and homogeneous inorganic conversion layer formation on the one hand and the local deposition of copper on defects in the conversion layer on the other hand. Empirically, it was found that such passive layers preferably have a layer support based on the elements titanium and / or zirconium of component (A) of at least 20 mg / m ² , more preferably of at least 40 mg / m ² , wherein at the same time based on the layer support preferably does not exceed 100 mg / m ² , more preferably 80 mg / m ² , but preferably at least 10 mg / m ² of copper deposited according to component (C). Accordingly, those agents according to the invention are preferred for which the molar ratio A: C of the total number of atoms of the elements titanium and / or zirconium of component (A) to the total number of copper atoms of component (C) is not less than 1: 3, preferably not less than 2: 3. If the ratio A: C falls short of the preferred range in the composition according to the invention, although sufficient inorganic conversion of the metallic surface can take place, the layer deposits with respect to copper are generally above 100 mg / m ² . In the extreme case, ie, significantly below the preferred ratio, the titanium and / or zirconium-based conversion is largely suppressed and wipeable coatings of amorphous metallic copper are the result.

Conversely, those agents according to the invention are preferred in which the ratio A: C of the total number of atoms of the elements titanium and / or zirconium the component (A) to the total number of copper atoms of component (C) does not exceed values for which, after contacting the agent with an iron surface, preferably with a carbon steel surface at a treatment time of 90 s and a treatment temperature of 30 ° C on this one layer of less than 20 mg / m ² based on the elements of component (A) selected from titanium and / or zirconium or more than 100 mg / m ² based on the element copper of component (C) results ,

Water-soluble compounds according to the invention corresponding to components (A) - (D) are characterized by being themselves in chemical equilibrium in aqueous solution with ionic species containing the respective named elements or with ionic species of the named elements themselves. The resulting in the aqueous solution chemical equilibrium between ionic species and undissociated water-soluble compound according to the components (A) - (D) must be qualitatively detectable by conventional methods, i. the ionic species must be present in the aqueous phase as such at least in an analytically determinable amount. By contrast, water-dispersible compounds of the invention corresponding to component (D) are characterized solely by their ionogenic structure and contain at least one of the respective named elements according to component (D) as an ionic constituent in an inorganic matrix. The proportion of the ionic species in the aqueous phase is predetermined by the solubility product of the water-dispersible compound.

Preferred water-soluble compounds of component (A) are compounds which dissociate in aqueous solution into anions of fluorocomplexes of the elements titanium and / or zirconium. Such preferred compounds are, for example, H ₂ ZrF ₆ , K ₂ ZrF ₆ , Na ₂ ZrF ₆ and (NH ₄ ) ₂ ZrF ₆ and the analogous titanium compounds. Such fluorine-containing compounds according to component (A) are simultaneously inventive water-soluble compounds according to component (B) and vice versa. Also fluorine-free compounds of the elements titanium and / or zirconium can be used according to the invention as water-soluble compounds according to component (A), for example (NH ₄ ) ₂ Zr (OH) ₂ (CO ₃ ) ₂ or TiO (SO ₄ ).

Preferred water-soluble compounds of component (B) which serve as a source of fluoride ions are, in addition to the fluorometallates already mentioned, hydrogen fluoride, alkali fluorides, ammonium fluoride and / or ammonium bifluoride.

Preferred water-soluble compounds of component (C) which release copper ions are all water-soluble copper salts containing no chloride ions. Particularly preferred are copper sulfate, copper nitrate and copper acetate.

Water-soluble compounds of component (D), which release metal ions, but do not constitute a source of fluoride ions, containing at least one metal atom selected from the group consisting of calcium, aluminum and / or iron, more preferably only the aluminum and / or release iron ions and in particular those which release exclusively aluminum ions.

These include all water-soluble salts of the aforementioned metals according to component (D), which contain neither fluoride nor chloride ions. By way of example, typical compounds according to component (D) may be mentioned at this point: calcium citrate, aluminum nitrate, iron (III) nitrate, iron (II) sulfate.

Preferred water-dispersible compounds of component (D) are compounds based on silicates containing aluminum, more preferably compounds of aluminum silicates with a ratio of aluminum to silicon atoms of at least 1: 3. In particular, aluminum silicates are the Molar formula (Na, K) _x (Ca, Mg) _1-x Al _2-x Si _{2 + x} O ₈ (where 0 ≤ x ≤ 1) is preferred, wherein the compound is preferably a zeolite with respect to their crystal morphology.

In principle, preference is given to those water-dispersible compounds of component (D) whose average particle diameter does not exceed 100 nm, particularly preferably 20 nm.

It is found that a higher relative proportion of aluminum, in particular the relative proportion of cations of aluminum, in the agent according to the invention increasingly inhibits the titanium- and / or zirconium-based conversion layer formation, so that in the treatment of iron surfaces, preferably of unalloyed steel surfaces Such a chromium-free agent tends to achieve lower coating deposits, based on the elements titanium and / or zirconium, which may be insufficient for adequate corrosion protection.

Furthermore, preference is given to those chromium-free compositions according to the invention in which the total content of fluorine atoms corresponding to component (B) is limited to 3 g / l, preferably to 2 g / l and more preferably to 1 g / l. Higher levels of fluorine are uneconomical because of the then significant levels of compounds according to component (D) and increase the operating costs of the conversion baths due to the inevitable additional regeneration and reprocessing measures.

The present invention is further characterized in that the chromium-free agent is not an additional polymeric agent for effective passivating treatment Must contain connections. However, small amounts of organic polymers such as derivatives of polyacrylates, polyvinyl alcohols, polyvinylphenols, polyvinylpyrrolidones or block copolymers consisting of structural units of the aforementioned polymers may be useful for the stability of compositions of the invention containing water-dispersible compounds according to component (D). It is therefore preferred that the total content of organic polymers in the composition according to the invention is less than 50 ppm, preferably less than 10 ppm and more preferably less than 1 ppm. In a specific embodiment, the agent according to the invention contains no organic polymer.

A proportion of phosphate anions in the composition according to the invention generally results in the treatment of metallic surfaces to phosphate-containing conversion layers containing a high proportion of bonded metal cations of the respective pickled substrate, especially zinc and iron cations. Such passive layers also have anti-corrosive properties, but are significantly different from titanium and / or zirconium-based conversion layers based on phosphate-free agents of the invention. In addition, the synergistic effect in the conversion layer structure in the presence of copper ions according to component (B), which is found especially in phosphate-free compositions of the invention and there causes increased corrosion protection and improved adhesion properties to organic cover layers, less pronounced in phosphate-containing inventive agents , An additional disadvantage of phosphate-containing agents according to the invention is the increased formation of sludge due to the local precipitation of sparingly soluble phosphates.

In a further preferred embodiment, the agent according to the invention therefore contains less than 5 ppm and particularly preferably no oxo anions of phosphorus.

The pH of the agent according to the invention is preferably not less than 2.5, more preferably not less than 3.5, but wherein a pH of preferably 5, more preferably 4.5 is not exceeded. Preferably, the pH is adjusted to the said acidic range by using, as component (A) or component (B), the fluoro-complexes of the elements titanium and / or zirconium at least partially in the form of an acid. However, it can also be adjusted by another acid, for example nitric acid and sulfuric acid. In addition, if it is desired to use the agent of the invention at higher pH, the pH may be adjusted accordingly by the addition of alkali metal hydroxides or carbonates, ammonia or organic amines.

In a further preferred embodiment of the composition according to the invention, a buffer system which has at least one protolysis equilibrium with a pK value in the range from 2.5 to 5 is additionally contained for adjusting the total acid content. As a buffer system for said pH range, an acetic acid / acetate buffer is particularly suitable. Another suitable buffer system based on potassium hydrogen phthalate. An increase in the total acid content by the addition of a buffer system increases the stability of the agent according to the invention and facilitates the pH fixation of the agent. The adjustment of the agent according to the invention to a defined pH value is necessary when using it, for example as a dip bath in a continuous process for the corrosion-protective treatment of metallic components for a constant quality of the conversion layer.

It is found that such a buffer capacity is sufficient, at which the pH of the agent according to the invention in the preferred pH range of 2.5 to 5.5 with an entry of one Val acid or lye per liter of solution is preferably no longer changed as 0.2 units.

Such a buffer capacity of the agent according to the invention is also present when the total acid content based on the total fluorine content is preferably not less than 5 points, more preferably not less than 6 points, but preferably not more than 10 points per 100 ppm fluorine. In addition to the already mentioned components of the agent according to the invention, the aqueous treatment solution may contain compounds which are used as so-called "accelerators" in the layer-forming phosphating. These accelerators have the property of trapping hydrogen atoms which form during the pickling attack of the acid on the metal surface. This reaction, also referred to as "depolarization", facilitates the attack of the acidic treatment solution on the metal surface and thereby accelerates the formation of the corrosion protection layer. A non-exhaustive list of preferred accelerators in the respective preferred concentration ranges is given below: 0.05 to 2 g / l m-nitrobenzenesulfonate ions, 0.1 to 10 g / l Hydroxylamine in free or bound form, 0.05 to 2 g / l m-nitrobenzoate ions, 0.05 to 2 g / l pN itrophenol, 1 to 70 mg / l Hydrogen peroxide in free or bound form, 0.05 to 10 g / l organic N-oxides 0.1 to 3 g / l nitroguanidine 1 to 500 mg / l Nitrite ions 1 to 1000 mg / l Nitrate ions 0.5 to 5 g / l Chlorate ions.

The agent of the present invention can be prepared on-site by dissolving said components (A) - (D) in water and adjusting the pH. However, this procedure is unusual in practice. Instead, in practice, aqueous concentrates are usually provided, from which the ready-to-use chromium-free agent is prepared on site by dilution with water and, if necessary, adjusting the pH. Accordingly, an aqueous concentrate which when diluted with water includes an acidic, chromium-free, by a factor of about 10 to about 100, more preferably a factor in the range of about 20 to about 50 and, if necessary, after adjusting the pH. aqueous solution according to the above description of the invention, also forms the subject of the present invention.

For stability reasons, such concentrates are often adjusted so that when diluting with water, the pH is not directly within the required range. In this case, after diluting with water, adjust the pH either down or up. The adjustment of the pH is carried out as previously described by adding suitable acids or bases.

In a further aspect, the present invention relates to a process for the anticorrosive conversion treatment of metallic surfaces, wherein the cleaned metallic surface is brought into contact with the aqueous chromium-free agent according to the invention.

This can be done, for example, by immersion in the treatment solution ("immersion process") or by spraying ("spraying process") with the chromium-free agent. The temperature of the composition according to the invention is preferably in the range of 15 to 60 ° C, in particular in the range of 25 to 50 ° C. The time required for treatment is a time interval which is matched to the convection in the bath system and typical for the composition of the metallic component to be treated. However, the contact time with the chromium-free agent is preferably at least 30 seconds, more preferably at least 1 minute, but should preferably be 10 minutes , more preferably 5 minutes. After this contact is preferably rinsed with water, especially with demineralized water.

The metal surfaces to be treated are previously freed of oil and grease residues in a cleaning step. At the same time a reproducible metal surface is produced, which ensures a consistent layer quality after the conversion treatment with the agent according to the invention. This is preferably an alkaline cleaning with commercially available products known to the person skilled in the art.

As a metal surface of the present invention surfaces of iron, steel, galvanized and alloy-iron and steel, which are obtainable for example under the commercial name Galfan ^®, Galvalume ^{®, ®} galvannealed within the meaning. The metallic surfaces which can be pretreated with the agent according to the invention to protect against corrosion also include aluminum and zinc as well as the respective alloys having an aluminum or zinc alloy content of at least 50 at.%. The metallic surface treated in the method according to the invention is preferably a "bare" metal surface. By "bare" metal surfaces are meant metal surfaces that do not yet carry a corrosion-protective coating. Thus, the method according to the invention is the first or only treatment step which produces a corrosion protection layer, which in turn can serve as the basis for a subsequent coating. It is therefore not a post-treatment of a previously generated corrosion protection layer such as a phosphate layer.

According to the invention, according to this further aspect of the invention, no measures are required and should preferably even be avoided by which the metal surface is dried after contact with the chromium-free agent and before coating with a dip paint, for example a cathodic electrodeposition paint. However, unintentional drying may occur during system downtime when the treated metal surface, such as an automobile body or part thereof, is in the air between the bath containing the agent of the invention and the dip bath. However, this unintentional drying is harmless.

According to the invention, immersion paint refers to those aqueous dispersions of organic polymers which are applied to the metal surface in the immersion process both without external current, ie self-deposited, and those in which coating with the paint from the aqueous phase takes place by applying an external voltage source.

Furthermore, the present invention comprises a metallic substrate which has been treated with the agent according to the invention in accordance with the method described above, the surface of the metallic substrate having a titanium and / or zirconium deposit of preferably not less than 20 mg / m ² and preferably not more than 150 mg / m ² . Here, such metallic substrates are particularly preferred, in which the layer based on copper pad does not exceed 100 mg / m ^2, preferably 80 mg / m ^2, but a minimum of 10 mg / m ² of copper deposited.

The use according to the invention of such metallic substrates in industrial processes for surface refinement by the subsequent application of a multilayer system is encompassed by the present invention.

Furthermore, according to the underlying invention, conversion-treated metallic materials, components and composite structures are used in the manufacture of semi-finished products, in automotive production in body construction, in shipbuilding, in construction and in the field of architecture as well as for the production of white goods and electronic housings.

The following exemplary embodiments show the technical advantages of the process according to the invention or of the novel chromium-free composition according to the invention.

The aqueous chromium-free composition according to the invention and the corresponding process sequence for the conversion treatment of metallic surfaces were tested on cold rolled steel test sheets (CRS ST1405, Sidca or MBS 25, Chemetall).

In the following, the sequence of processes for the treatment according to the invention of the sample sheets, as is in principle also customary in the automotive body production, is reproduced.

For pretreatment, the sheets were first cleaned alkaline at 60 ° C for 5 min and degreased. For this purpose surfactant mixtures of commercial products of the applicant were used: a mixture containing 3% Ridoline ^® 1574A and 0.3% Ridosol ^® 1270. This was followed by a rinsing with hot water followed by a further rinse with deionized water (κ <1 μScm ^-1) before the cold-rolled steel sheets were treated with a chromium-free agent at 30 ° C for 90 seconds.

To assess the quality of the conversion treatment, the freshly treated steel sheets were subjected to a "hot water test". In the "hot water test", the homogeneity of the conversion coating is checked and evaluated after treatment with the agent according to the invention. For this purpose, the freshly treated steel sheets were first blown dry, then immediately dipped at 20 ° C for 30 sec in process water and then dried in air.

According to the present invention, service water is the water which has a predetermined range of values for specific characteristics selected from the conductivity, the pH, the chloride and nitrate ion content and the copper content. In general, domestic hot water for use in the "domestic water test" according to the invention must comply with the requirements of EU Directive 98/83 / EC, whereby in particular the chemical parameters for the process water listed in the following table are binding for the performance of the "domestic water test". are. parameter Key figures conductivity 500-900 μScm ^-1 at 20 ° C PH value 6.5-7.5 chloride <250 ppm nitrate <50 ppm copper <0.1 ppm Remaining heavy metals <500 ppb

• 0: keine sichtbare Rotrostbildung
• 1: kaum/sehr wenig Rotrost (< 10 %)
• 2: wenig Rotrost (< 20 %)
• 3: deutliche Rotrostbildung (< 30 %)
• 4: überwiegend Rotrost (> 50 %)

After the treatment of the steel sheets according to the "hot water test" as described above, the evaluation of the red rust formation follows according to the following scale:

• 0: no visible red rust formation
• 1: hardly / very little red rust (<10%)
• 2: little red rust (<20%)
• 3: distinct red rust formation (<30%)
• 4: predominantly red rust (> 50%)

Red rust refers to the red-appearing corrosion products of iron, typically iron oxide. The formation of red rust occurs almost instantaneously on exposure of iron in a humid atmosphere. Thus, a thin process water film on a surface of iron is sufficient to initiate the formation of red rust. The formation of red rust, however, comes to a standstill in a dry atmosphere, so that a good assessment of the homogeneity of a corrosion-protective conversion layer formation on iron surfaces via the induced formation of red rust is possible. If the steel surface treated with the chromium-free agent yields a homogeneous, closed conversion layer, the formation of red rust is minimal or invisible to the human eye. Conversely, in the "process water test" macroscopic defects are formed Insufficient layer formation or clearly visible on too thin passive layers Red rust.

Table 1 shows chromium-free zirconium-based anticorrosive pretreatment agents for metal surfaces applied to cold-rolled steel according to the method described above.

Only examples B3-B6 are according to the invention.

1. (A) H₂ZrF₆
2. (B) H₂ZrF₆, (NH₄)HF₂
3. (C) Cu(NO₃)₂·3H₂O
4. (D) Fe(NO₃)₃·9H₂O [Tabellen 1, 3] oder Al(NO₃)₃·9H₂O [Tabelle 2]

The respective components (A) - (D) according to the terminology of the present invention are:

1. (A) H ₂ ZrF ₆
2. (B) H ₂ ZrF _6, (NH ₄₎ HF ₂
3. (C) Cu (NO ₃ ) ₂ .3H ₂ O
4. (D) Fe (NO ₃ ) ₃ .9H ₂ O [Tables 1, 3] or Al (NO ₃ ) ₃ .9H ₂ O [Table 2]

On the basis of Table 1, it is first clear that chromium-free compositions which do not contain copper ions (VB1), while providing a sufficient layer coverage of> 20 mg / m ² on the steel surface, however, such a conversion layer can not completely suppress the occurrence of red rust , In contrast, in the presence of copper ions in the middle (B1), both zirconium and copper are incorporated in the passive layer, whereby zirconium layer deposits are achieved which clearly exceed those of the layerings achieved by copper-free compositions (VB1). This synergistic effect and the simultaneous deposition of copper cause that in the "hot water test" the formation of red rust hardly appears or even fails. The synergistic effect, which is that the conversion layer formation is accelerated, is independent of the total amount of zirconium (B2) at a constant molar ratio of zirconium to copper fraction (A: C). At least with regard to the formation of red rust after the "hot water test", higher proportions of copper deposited in the conversion layer behave indifferent, as can be seen from the comparison of the inventive examples B1 and B2.

Another aspect of the present invention consists in the total fluoride content relative to the proportion of "fluoride scavenger" (component D), which according to the invention must not fall below a certain value. For this purpose, the examples VB2 and B1 is clear in comparison that the doubled fluoride content (component B) (to a complete inhibition of the conversion layer formation while maintaining the same amount of iron ions (VB2) layer pad Zr: <1.5 mg / m ² ) leads and only metallic copper deposits on the steel surface (coating layer Cu: 67 mg / m ² ). The molar ratio D: B according to the invention of the "fluoride scavenger" iron to the total fluorine content of 1: 7.6 is significantly below the actual ratio 1:22.

In particular, for chromium-free compositions according to the invention containing exclusively aluminum as the "fluoride scavenger" (component D), the relative content of aluminum based on the fluorine content determines the quality of the conversion layer formation. Table 2 lists this chromium-free agent with increasing zirconium content (component A) and at the same time decreasing proportion of copper ions (component C), the example according to the invention has a molar ratio D: B of aluminum to fluorine of 1: 4. For the treatment of steel sheets, satisfactory results with regard to the "hot water test" result only when the agents B3-B5 according to the invention are used. If the target value for the molar ratio of D: B in the chromium-free agent is undershot, as already shown in Table 1 under VB2, the conversion layer formation is inhibited, so that after the "hot water test" a significant red rust formation is detected (VB1-VB3) ,

At the same time it should be noted that the synergistic effect of copper ions drops significantly as soon as the molar ratio of zirconium to copper in the composition according to the invention is greatly increased (B6). In this case, both the achieved coating layer based on zirconium as well as on copper is reduced in such a way that noticeable red rust is formed in the "process water test" (B6).

The results from Table 3 of conversion treated steel surfaces in the corrosive paint adhesion and in the stone impact test confirm that both at very high (B7) and low (B11) relative copper contents in the chromium-free agent, the paint adhesion is positively influenced. All compositions according to the invention in which the molar ratio A: C varies between 1: 14 and 37: 1 are superior to copper-free agents (VB7) for conversion treatment, as long as the total content of zirconium (component A) is sufficient on average to undergo conversion the surface at optimally adjusted molar ratio D: B of "fluoride scavenger" to cause fluorine content (VB6).

Claims (14)

1. An aqueous chromium-free agent for the corrosion-protective conversion treatment of metallic surfaces, containing

   (A) one or more water-soluble compounds containing at least one atom selected from the elements titanium and/or zirconium, wherein the total concentration of these elements is not less than 2.5·10^-4 mol/L, but is not greater than 2.0·10^-2 mol/L,

   (B) one or more water-soluble compounds, as a source of fluoride ions, containing at least one fluorine atom,

   wherein the agent contains said elements of the respective components (A) and (B) in a molar ratio A : B of 1 : z, where z is a real number and is greater than 6,
   characterized in that the agent additionally contains

   (C) one or more water-soluble compounds, containing at least one copper atom, which release copper ions, and

   (D) one or more water-soluble and/or water-dispersible compounds which release metal ions but which are not a source of fluoride ions, and which contain at least one metal atom selected from the group comprising calcium, aluminum, and/or iron,

   wherein the molar ratio D : B of the total number of metal atoms of component (D) to the total number of fluorine atoms of component (B) is not less than $\frac{z-6}{4z},$

   

   
   wherein component (D) is composed at least of a water-soluble and/or water-dispersible compound containing at least one aluminum atom, and the molar ratio of the total number of aluminum ions of component (D) to the total number of fluorine atoms of component (B) is not greater than $\frac{z-6}{z}\mathrm{.}$

   
2. The agent according to Claim 1, characterized in that the molar ratio D : B of the total number of metal atoms of component (D) to the total number of fluorine atoms of component (B) is not less than a value for which, after the agent is brought into contact with an iron surface for a treatment period of 90 s and a treatment temperature of 30°C, a coating layer of less than 20 mg/m², based on the elements of component (A) selected from titanium and/or zirconium, results on the iron surface.
3. The agent according to one or both of the preceding claims, characterized in that the molar ratio D : B of the total number of metal atoms of component (D) to the total number of fluorine atoms of component (B) is not less than $\frac{z-6}{3z},$

   

   preferably not less than $\frac{z-6}{2z}\mathrm{.}$

   
4. The agent according to one or more of the preceding claims, characterized in that the molar ratio A : C of the total number of atoms of the elements titanium and/or zirconium of component (A) to the total number of copper atoms of component (C) is not less than 1 : 3, preferably not less than 2 : 3.
5. The agent according to one or more of the preceding claims, characterized in that the ratios D : B and A : C in each case do not exceed values which, after which the agent is brought into contact with an iron surface, preferably an unalloyed steel surface, for a treatment period of 90 s and a treatment temperature of 30°C, a coating layer of less than 20 mg/m², based on the elements of component (A) selected from titanium and/or zirconium, results on the iron surface.
6. The agent according to one or more of the preceding claims, characterized in that component (D) is composed at least of a water-dispersible compound based on silicates containing aluminum, preferably aluminum silicate, having a ratio of aluminum atoms to silicon atoms of at least 1 : 3.
7. The agent according to one or more of the preceding claims, characterized in that the total content of fluorine atoms corresponding to component (B) does not exceed 3 g/L, preferably 2 g/L, particularly preferably 1 g/L.
8. The agent according to one or more of the preceding claims, characterized in that the total content of oxoanions of phosphorus is less than 1 ppm.
9. The agent according to one or more of the preceding claims, characterized in that the pH of the agent is not less than 2.5, preferably not less than 3.5, but does not exceed a value of 5, preferably 4.5.
10. The agent according to Claim 8, characterized in that for setting the overall acid content, a buffer system is additionally contained which has at least a protolytic equilibrium having a pK value in the range of 2.0 to 5.0.
11. A method for the corrosion-protective conversion treatment of metallic surfaces which are selected from surfaces of iron, steel, galvanized and alloy galvanized iron and steel, aluminum, and/or zinc, and the respective alloys having an alloy content of aluminum and/or zinc of at least 50 at.-%, characterized in that the metallic surface is brought into contact with the aqueous chromium-free agent according to one or more of the preceding claims.
12. The method according to Claim 11, characterized in that the metallic surface is not dried after the agent is brought into contact with the metallic surface, or before a further coating with a dip coating.
13. A metallic substrate which has been treated according to one or both of Claims 11 and 12, and which has a titanium and/or zirconium coating of not less than 20 mg/m², but not greater than 150 mg/m², on its surface.
14. Use of a metallic substrate according to Claim 13 for the manufacture of white goods, electronic housings, semi-finished products, bodies in automobile manufacturing, and in the construction industry and in the field of architecture.