EP3676419B1 - Improved method for nickel-free phosphating of metallic surfaces - Google Patents

Description

The present invention relates to a process for the essentially nickel-free phosphating of a metallic surface using a special cleaning composition and the use of this process in the automotive industry.

Phosphate coatings on metallic surfaces are known from the prior art. Such coatings serve to protect metal surfaces from corrosion and also serve as an adhesion promoter for subsequent coats of paint.

Such phosphate coatings are primarily used in the automotive and general industries.

In addition to powder paints and wet paints, the subsequent paint layers are primarily cathodically deposited electrophoretic paints (KTL). Since a current must flow between the metallic surface and the treatment bath during the deposition of KTL, it is important to set a defined electrical conductivity of the phosphate coating in order to ensure efficient and homogeneous deposition.

Therefore, phosphate coatings are usually applied using a nickel-containing phosphating solution. The nickel deposited elementally or as an alloy component, e.g. Zn/Ni, ensures suitable conductivity of the coating during the subsequent electrocoating.

However, due to their high toxicity and environmental damage, nickel ions are no longer desirable as a component of treatment solutions and should therefore be avoided if possible or at least reduced in content.

The use of nickel-free or low-nickel phosphating solutions is known in principle. However, this is limited to certain substrates such as steel. A nickel-free phosphating solution is available from the DE19854431 A1 known.

With the low-nickel or nickel-free systems mentioned, poor corrosion protection and paint adhesion values can also result under given KTL deposition conditions due to a sub-optimal substrate surface.

The object of the present invention was therefore to provide a method with which metallic surfaces can be phosphated essentially without nickel, while avoiding the aforementioned disadvantages of the prior art.

This task is solved by a method according to claim 1 and the use according to claim 10.

1. i) mit einer alkalischen, wässrigen Reinigerzusammensetzung, welche mindestens ein wasserlösliches Silikat enthält und dann
2. ii) mit einer sauren, wässrigen, im Wesentlichen nickelfreien Phosphatierzusammensetzung, welche Zinkionen, Manganionen und Phosphationen umfasst.

In the method according to the invention for essentially nickel-free phosphating of a metallic surface, a metallic surface is successively treated with the following compositions:

1. i) with an alkaline, aqueous cleaning composition which contains at least one water-soluble silicate and then
2. ii) with an acidic, aqueous, substantially nickel-free phosphating composition comprising zinc ions, manganese ions and phosphate ions.

Definitions:

On the one hand, an uncoated metallic surface, but on the other hand, an already conversion-coated metallic surface can also be treated with the method according to the invention. When we talk about a “metallic surface” below, it should always include a metallic surface that has already been conversion-coated. However, it is preferably an uncoated metallic surface.

For the purposes of the present invention, an “aqueous composition” refers to a composition which contains at least some, preferably most, i.e. more than 50% by weight, water as a solvent/dispersion medium. In addition to dissolved components, it can also include coarsely dispersed components. It can therefore be, for example, an emulsion. However, it is preferably a solution, i.e. a composition that does not contain any coarsely dispersed components.

When we talk about a "water-soluble silicate" below, we mean a silicate that has a water solubility (in demineralized water) of at least 1 mg/l at 25 °C, preferably at least 10 mg/l, more preferably at least 100 mg/l, more preferably at least 1 g/l, more preferably at least 10 g/l, more preferably at least 100 g/l, more preferably at least 200 g /l, more preferably of at least 300 g/l and particularly preferably of at least 350 g/l. The silicate can also be present as a colloidal solution.

If a composition contains less than 0.01 g/L nickel ions, it should be considered “substantially nickel-free” for the purposes of the present invention.

For the purposes of the present invention, “phosphate ions” also means hydrogen phosphate, dihydrogen phosphate and phosphoric acid. In addition, pyrophosphoric acid and polyphosphoric acid and all their partially and completely deprotonated forms should be included.

For the purposes of the present invention, “metal ion” is understood to mean either a metal cation, a complex metal cation or a complex metal anion.

The metallic surface is preferably steel, a steel alloy, hot-dip galvanizing, electrolytic galvanizing, a zinc alloy such as Zn/Fe or Zn/Mg, aluminum or an aluminum alloy. Hot-dip galvanizing and electrolytic galvanizing are particularly applied to steel. In particular, the metallic surface is at least partially galvanized.

The method according to the invention is particularly suitable for multi-metal applications, in particular for metallic surfaces which, in addition to galvanizing on steel, preferably hot-dip galvanizing and electrolytic galvanizing, contain aluminum and/or an aluminum alloy, preferably an aluminum alloy.

According to the invention, the metallic surface is first cleaned (step i), in particular degreased, in an alkaline, aqueous cleaning composition before treatment with the acidic, aqueous, essentially nickel-free phosphating composition (step ii). If necessary, an acidic or neutral pickling composition can also be used for this purpose.

The cleaning composition can be obtained from a concentrate by diluting it with a suitable solvent, preferably water, preferably by a factor between 1.5 and 1000, more preferably between 50 and 200, and if necessary adding a pH-modifying substance.

The at least one water-soluble silicate contained in the cleaning composition results in a better cleaning effect and reduces the pickling attack in the cleaning bath (inhibiting effect).

According to the invention, the at least one water-soluble silicate comprises at least one water glass, in particular a lithium water glass, a soda water glass and/or a potassium water glass, particularly preferably a soda water glass and/or a potassium water glass, and/or at least one metasilicate such as disodium metasilicate (Na ₂ SiO ₃ ).

Particularly preferably, the at least one water-soluble silicate comprises a soda water glass or a potassium water glass.

The soda water glass is preferably one with a molar Na ₂ O:SiO ₂ ratio in the range from 1 to 4. The potassium water glass is also preferably one with a molar K ₂ O:SiO ₂ ratio in the range from 1 to 4.

According to the invention, the at least one water-soluble silicate is present in a total concentration in the range from 0.01 to 15 g/l, preferably from 0.2 to 13 g/l and particularly preferably from 0.5 to 10 g/l.

In addition to the at least one water-soluble silicate, the cleaning composition can contain at least one cationic, nonionic and/or anionic surfactant and/or other additives, in particular complexing agents, oxidizing agents, oils and/or auxiliary substances such as solubilizers, borate and/or carbonate.

The addition of at least one complexing agent and/or at least one oxidizing agent has proven to be advantageous in terms of the corrosion protection and paint adhesion values achieved and is therefore preferred.

Complexing agents contained in the cleaning composition cause a complexation of water hardness and dissolved cations, which are caused by the pickling attack go into solution or are present in the cleaning bath.

Preferred complexing agents are, on the one hand, phosphorus-containing complexing agents.

These are in particular phosphate-based complexing agents - preferably condensed phosphates such as pyrophosphates, tripolyphosphates and other polyphosphates - as well as phosphonic acids such as 1-hydroxyethane-(1,1-diphosphonic acid) (HEDP) and their salts.

The phosphorus-containing, in particular the phosphate-based, complexing agents are preferably in a total concentration in the range from 0.01 to 15 g/l, more preferably from 0.05 to 13 g/l and particularly preferably from 0.1 to 10 g/l (calculated as tetrapotassium pyrophosphate).

On the other hand, preferred complexing agents are hydroxycarboxylic acids, which have at least one hydroxyl group and at least one carboxyl group, and their salts, in particular sugar acids and their salts, particularly preferably heptonate and gluconate. Gluconate is particularly preferred. Such complexing agents are preferably present in a total concentration in the range from 0.01 to 6 g/l, more preferably from 0.05 to 5 g/l and particularly preferably from 0.1 to 4 g/l (calculated as sodium gluconate).

1. i) Tetrakaliumpyrophoshat und Gluconat,
2. ii) Pentanatriumtripolyphosphat und Gluconat.

According to a particularly preferred embodiment, the cleaning composition contains at least one phosphorus-containing complexing agent, in particular a pyrophosphate and/or a tripolyphosphate, and at least one hydroxycarboxylic acid or its salt, in particular gluconate. Particularly preferred combinations are:

1. i) tetrapotassium pyrophosate and gluconate,
2. ii) Pentasodium tripolyphosphate and gluconate.

A preferred oxidizing agent is nitrite. The oxidizing agents are preferably present in a total concentration in the range from 10 to 100 mg/l, particularly preferably from 20 to 50 mg/l (calculated as nitrite).

Preferably no iron ions, in particular no iron(III) ions, are added to the cleaning composition. In this case, any iron ions present in the cleaning bath come exclusively from the treated metallic one Surface.

To adjust the alkalinity of the cleaning composition, on the one hand, in particular caustic soda, potassium hydroxide, caustic soda or caustic potash, on the other hand, in particular phosphoric acid can be used.

According to the invention, the pH value of the cleaning composition is in the range from 10.7 to 12.0, preferably from 11.0 to 12.0, more preferably from 11.3 to 12.0 and particularly preferably in the range from 11.5 to 12.0.

The cleaning composition preferably has a temperature in the range from 35 to 70, more preferably from 40 to 65 and particularly preferably from 45 to 60 ° C. The metallic surface is treated with the cleaning composition preferably for 30 to 600, particularly preferably for 60 to 480 and very particularly preferably for 90 to 360 seconds, preferably by dipping or spraying, or a combination of both.

According to a preferred embodiment, the metallic surface is first sprayed with the cleaning composition for 30 to 90 seconds and then immersed in it for 100 to 300 seconds.

After cleaning/pickling and before treating the metallic surface with the phosphating composition, at least one rinsing of the metallic surface with water advantageously takes place, with the water optionally also containing an additive dissolved in water, such as. B. a nitrite or surfactant can be added.

Before treating the metallic surface with the phosphating composition, it is also advantageous to treat the metallic surface with an activating composition. The activation composition serves to deposit a large number of the finest phosphate particles as seed crystals on the metallic surface. In the subsequent process step, these help to form a particularly crystalline phosphate layer with the highest possible number of densely arranged fine phosphate crystals or a largely closed phosphate layer in contact with the phosphating composition - preferably without intermediate rinsing.

Particularly suitable activation compositions are alkaline compositions based on titanium phosphate or zinc phosphate.

However, it can also be advantageous to add activating agents, in particular titanium phosphate or zinc phosphate, to the cleaning composition, i.e. to carry out cleaning and activation in one step.

The acidic, aqueous, essentially nickel-free phosphating composition includes zinc ions, manganese ions and phosphate ions.

The phosphating composition can be obtained from a concentrate by diluting it with a suitable solvent, preferably water, by a factor between 1.5 and 100, preferably between 5 and 50, and if necessary adding a pH-modifying substance.

The phosphating composition preferably comprises the following components in the following preferred and particularly preferred concentration ranges: Zn 0.3 to 3.0 g/l 0.5 to 2.0 g/l Mn 0.3 to 2.0 g/l 0.5 to 1.5 g/l Phosphate (calculated as P ₂ O ₅ ) 8 to 25 g/l 10 to 18 g/l free fluoride 30 to 250 mg/l 50 to 180 mg/l Complex fluoride (calculated e.g. as SiF ₆ ^2- and/or BF ₄ ^- ) 0 to 5 g/l 0.5 to 3 g/l

With regard to the manganese ions, however, a concentration in the range of 0.3 to 2.5 g/l has already proven to be advantageous, and with regard to free fluoride, a concentration in the range of 10 to 250 mg/l has proven to be advantageous.

The complex fluoride is preferably tetrafluoroborate (BF ₄ ^- ) and/or hexafluorosilicate (SiF ₆ ^2- ).

Particularly when treating aluminum and/or galvanized material, a content of complex fluoride and simple fluoride, for example sodium fluoride, in the phosphating composition is advantageous.

Al ³⁺ is a bath poison in phosphating systems and can be removed from the system by complexing with fluoride, for example as cryolite. Complex fluorides are added to the bath added as a "fluoride buffer", otherwise the fluoride content would drop quickly and no coating would take place. Fluoride supports the formation of the phosphate layer and indirectly leads to an improvement in paint adhesion and corrosion protection. Complex fluoride also helps to avoid defects such as specks on galvanized material.

Particularly when treating aluminum, it is also advantageous if the phosphating composition contains iron(III) ions. The iron(III) ions are preferably added to the phosphating composition. It is preferred to add iron(III) ions in the range from 0.001 to 0.2 g/l, more preferably from 0.001 to 0.1 g/l, more preferably from 0.005 to 0.1 g/l, particularly preferably from 0.005 to 0.05 g/l and most preferably from 0.005 to 0.02 g/l.

In addition, the phosphating composition preferably contains at least one accelerator selected from the group consisting of the following compounds in the following preferred and particularly preferred concentration ranges: Nitroguanidine 0.2 to 3.0 g/l 0.2 to 1.55 g/l _{H2O2 _} 10 to 100 mg/l 15 to 50 mg/l _{Nitroguanidine} / _H2O2 0.2 to 2.0 g/l / 10 to 50 mg/l 0.2 to 1.5 g/l / 15 to 30 mg/l nitrite 30 to 300 mg/l 90 to 150 mg/l Hydroxylamine 0.1 to 5 g/l 0.4 to 3 g/l

With regard to nitroguanidine, however, a concentration in the range of 0.1 to 3.0 g/l has already proven to be advantageous, and with regard to H ₂ O ₂ a concentration in the range of 5 to 200 mg/l has proven to be advantageous.

Very particularly preferably, the at least one accelerator is H ₂ O ₂ .

However, the phosphating composition preferably contains less than 1 g/l, more preferably less than 0.5 g/l, particularly preferably less than 0.2 g/l and most preferably less than 0.1 g/l nitrate.

Particularly on a galvanized surface, the nitrate in the phosphating composition causes an additional acceleration Layer formation reaction, which leads to lower layer weights but above all reduces the incorporation of manganese into the crystal. However, if the manganese content of the phosphate coating is too low, this will affect its alkali resistance.

Alkaline resistance in turn plays a crucial role in subsequent cathodic electrocoating. This results in an electrolytic splitting of water on the substrate surface: hydroxide ions are formed. This causes the pH value at the interface of the substrate to increase. Only in this way can the electrophoretic paint be agglomerated and deposited. However, the increased pH can also damage the crystalline phosphate layer.

The phosphating composition preferably has a temperature in the range from 30 to 55°C.

Furthermore, the phosphating composition can be characterized by the following preferred and particularly preferred parameter ranges: FS 0.3 to 2.0 0.7 to 1.6 FS (dil.) 0.5 to 8 1 to 6 GSF 12 to 28 22 to 26 G.S 12 to 45 18 to 35 S value 0.01 to 0.2 0.03 to 0.15 temperature 30 to 50°C 35 to 45°C

With regard to the FS parameter, however, a value in the range of 0.2 to 2.5 has already proven to be advantageous, and with regard to the temperature, a value in the range of 30 to 55 °C has proven to be advantageous.

Here, "FS" stands for free acid, "FS (diluted)" for free acid (diluted), "GSF" for total acid according to Fischer, "GS" for total acid and "S-value" for acid value.

The determination of these parameters is carried out as part of the analytical control of the phosphating chemicals and serves the ongoing monitoring of the working phosphating bath (cf. W. Rausch "The phosphating of metals", Eugen G. Leuze Verlag, 3rd edition, 2005, chapter 8, p. 332 ff .):
Free acid (FS):
(Please refer W. Rausch "The phosphating of metals", Eugen G. Leuze Verlag, 3rd edition, 2005, chapter 8.1, pp. 333-334 )

To determine the free acid, 10 ml of the phosphating composition are pipetted into a suitable vessel, for example a 300 ml Erlenmeyer flask. If the phosphating composition contains complex fluorides, 2-3 g of potassium chloride are added to the sample. Then titrate to a pH of 3.6 using a pH meter and an electrode with 0.1 M NaOH. The amount of 0.1 M NaOH in ml used per 10 ml of the phosphating composition gives the value of the free acid (FS) in points.
Free acid (diluted) (FS (diluted)):
(Please refer W. Rausch "The phosphating of metals", Eugen G. Leuze Verlag, 3rd edition, 2005, chapter 8.1, pp. 333-334 )

To determine the free acid (diluted), 10 ml of the phosphating composition are pipetted into a suitable vessel, for example a 300 ml Erlenmeyer flask. Then 150 ml of demineralized water are added. Using a pH meter and an electrode, titrate with 0.1 M NaOH to a pH of 4.7. The amount of 0.1 M NaOH in ml used per 10 ml of the diluted phosphating composition gives the value of the free acid (diluted) (FS (dil.)) in points. The complex fluoride content can be determined via the difference to the free acid (FS). If this difference is multiplied by a factor of 0.36, the complex fluoride content is obtained as SiF ₆ ^2- in g/l.
Total acidity according to Fischer (GSF):
(Please refer W. Rausch "The phosphating of metals", Eugen G. Leuze Verlag, 3rd edition, 2005, chapter 8.2, pp. 334-336 )

Following the determination of the free acid (diluted), the diluted phosphating composition is titrated to a pH of 8.9 using a pH meter and an electrode with 0.1 M NaOH after adding potassium oxalate solution. The consumption of 0.1 M NaOH in ml per 10 ml of the diluted phosphating composition gives the total acid according to Fischer (GSF) in points. If this value is multiplied by 0.71, the total phosphate ion content is calculated as P ₂ O ₅ .
Total acid (GS):
(Please refer W. Rausch "The phosphating of metals", Eugen G. Leuze Verlag, 3rd edition, 2005, chapter 8.3, pp. 336-338 )

The total acid (GS) is the sum of the divalent cations contained as well as free and bound phosphoric acids (the latter are phosphates). It is determined by the consumption of 0.1 M NaOH using a pH meter and an electrode. To do this, 10 ml of the phosphating composition are pipetted into a suitable vessel, for example a 300 ml Erlenmeyer flask, and diluted with 25 ml of demineralized water. The mixture is then titrated with 0.1 M NaOH to a pH of 9. The consumption in ml per 10 ml of the diluted phosphating composition corresponds to the total acid score (GS).
Acid value (S value):
(Please refer W. Rausch "The phosphating of metals", Eugen G. Leuze Verlag, 3rd edition, 2005, chapter 8.4, p. 338 )

The so-called acid value (S value) stands for the ratio FS: GSF and is obtained by dividing the value of the free acid (FS) by the value of the total acid according to Fischer (GSF).

What was surprising was the further improvement in paint adhesion, especially on hot-dip galvanized surfaces, by setting an acid value in the range from 0.03 to 0.065, especially in the range from 0.04 to 0.06.

It has surprisingly been found that, particularly in the case of steel or hot-dip galvanizing as a metallic surface, a temperature of the phosphating composition of less than 45 ° C, preferably in the range between 35 and 45 ° C, leads to further improved corrosion and paint adhesion values.

The metallic surface is treated with the phosphating composition preferably for 30 to 480, particularly preferably for 60 to 300 and very particularly preferably for 90 to 240 seconds, preferably by dipping or spraying.

By treating the metallic surface with the phosphating composition, the following preferred and particularly preferred zinc phosphate layer weights are applied to the surface, depending on the surface being treated metallic surface (determined using X-ray fluorescence analysis (XRF)): Treated surface Zinc phosphate layer weight (g/m ² ) steel 0.5 to 6 1 to 5 Hot-dip galvanizing 1.0 to 6 1.5 to 5 electrolytic galvanizing 1.0 to 6 1.5 to 5 aluminum 0.5 to 6 1 to 5

After treatment, the metallic surface is preferably rinsed with the phosphating composition, more preferably rinsed with deionized water or city water.

According to the invention, the metallic surface that has already been treated with the phosphating composition, i.e. phosphate-coated, is further treated with an aqueous rinsing composition. The metallic surface is optionally dried before treatment with the rinsing composition.

The rinse composition can be obtained from a concentrate by diluting it with a suitable solvent, preferably water, by a factor between 1.5 and 1000, preferably between 5 and 700, and if necessary adding a pH-modifying substance.

By treating with the rinsing composition, the electrical conductivity of the phosphate-coated metal surface can be specifically adjusted by creating defined pores in the phosphate layer. The conductivity can be either greater than, equal to or less than that of a corresponding metal surface provided with a nickel-containing phosphate coating.

The set electrical conductivity of the phosphate-coated metal surface can be influenced by varying the concentration of a given metal ion or polymer in the rinsing composition.

According to one embodiment, the rinse composition contains at least one type of metal ion selected from the group consisting of the ions of the following metals in the following preferred, particularly preferred and very particularly preferred concentration ranges (all calculated as the corresponding metal): Mo 1 to 500 mg/l 10 to 250 mg/l 20 to 150 mg/l Cu 1 to 1000 mg/l 100 to 500 mg/l 150 to 225 mg/l Ag 1 to 500 mg/l 5 to 300 mg/l 20 to 150 mg/l Ow 1 to 500 mg/l 10 to 300 mg/l 20 to 200 mg/l Pd 1 to 200 mg/l 5 to 100 mg/l 15 to 60 mg/l Sn 1 to 500 mg/l 2 to 200 mg/l 3 to 100 mg/l Sb 1 to 500 mg/l 2 to 200 mg/l 3 to 100 mg/l Ti 20 to 500 mg/l 50 to 300 mg/l 50 to 150 mg/l Zr 20 to 500 mg/l 50 to 300 mg/l 50 to 150 mg/l Hf 20 to 500 mg/l 50 to 300 mg/l 50 to 150 mg/l

The metal ions contained in the rinsing composition separate either in the form of a salt, which contains the corresponding metal cation (e.g. molybdenum or tin) preferably in at least two oxidation states - in particular in the form of an oxide hydroxide, a hydroxide, a spinel or a defect spinel - or elementally on the surface to be treated (e.g. copper, silver, gold or palladium).

According to the invention, the metal ions are molybdenum ions. These are preferably added to the rinsing composition as molybdate, more preferably as ammonium heptamolybdate and particularly preferably as ammonium heptamolybdate x 7 H ₂ O. The molybdenum ions can also be added as sodium molybdate.

Molybdenum ions can, for example, also be added to the rinsing composition in the form of at least one salt containing molybdenum cations, such as molybdenum chloride, and then oxidized to molybdate by a suitable oxidizing agent, for example by the accelerators described above. In such a case, the rinse composition itself contains a corresponding oxidizing agent.

According to the invention, it contains molybdenum ions in combination with zirconium ions and optionally a polymer or copolymer, in particular selected from Group consisting of the polymer classes of polyamines, polyethyleneamines, polyanilines, polyimines, polyethyleneimines, polythiophenes and polypryrols as well as their mixtures and copolymers and polyacrylic acid, the content of molybdenum ions and zirconium ions each being in the range from 10 to 500 mg/l (calculated as metal). .

The molybdenum ion content is preferably in the range from 20 to 150 mg/l, particularly preferably from 25 to 100 mg/l and very particularly preferably from 30 to 75 mg/l and the zirconium ion content is in the range from 50 to 300 mg/l. l, particularly preferably from 50 to 150 mg/l.

Copper ions are preferably also present in the rinsing solution.

The rinse solution then preferably contains this in a concentration of 100 to 500 mg/l, more preferably 150 to 225 mg/l. According to a further embodiment, the rinse composition according to the invention contains at least one polymer selected from the group consisting of the polymer classes of polyamines, polyethyleneamines, polyanilines, polyimines, polyethyleneimines, polythiophenes and polypyroles as well as mixtures and copolymers thereof.

The at least one polymer is preferably in a concentration in the range from 0.1 to 5 g/l, more preferably from 0.1 to 3 g/l, more preferably from 0.3 to 2 g/l and particularly preferably in the range from 0.5 to 1.5 g/l (calculated as pure polymer).

Cationic polymers, in particular polyamines, polyethyleneamines, polyimines and/or polyethyleneimines, are preferably used as polymers. A polyamine and/or polyimine, very particularly preferably a polyamine, is particularly preferably used.

According to a third embodiment not according to the invention, the rinse composition according to the invention contains at least one type of metal ion selected from the group consisting of the ions of molybdenum, copper, silver, gold, palladium, tin, antimony, titanium, zirconium and hafnium and at least one polymer selected from the Group consisting of the polymer classes of polyamines, polyethyleneamines, polyanilines, polyimines, polyethyleneimines, polythiophenes and polypryrols and their Mixtures and copolymers, each in the following preferred, particularly preferred and very particularly preferred concentration ranges (polymer calculated as pure polymer and metal ions calculated as the corresponding metal). Mo 1 to 500 mg/l 10 to 250 mg/l 20 to 150 mg/l Cu 1 to 1000 mg/l 100 to 500 mg/l 150 to 225 mg/l Ag 1 to 500 mg/l 5 to 300 mg/l 20 to 150 mg/l Ow 1 to 500 mg/l 10 to 300 mg/l 20 to 200 mg/l Pd 1 to 200 mg/l 5 to 100 mg/l 15 to 60 mg/l Sn 1 to 500 mg/l 2 to 200 mg/l 3 to 100 mg/l Sb 1 to 500 mg/l 2 to 200 mg/l 3 to 100 mg/l Ti 20 to 500 mg/l 50 to 300 mg/l 50 to 150 mg/l Zr 20 to 500 mg/l 50 to 300 mg/l 50 to 150 mg/l Hf 20 to 500 mg/l 50 to 300 mg/l 50 to 150 mg/l polymer 0.1 g/l to 3 g/l 0.3 g/l to 2 g/l 0.5 to 1.5 g/l

Optionally, the at least one polymer is a cationic polymer, in particular a polyamine and/or polyimine, and the metal ions are copper ions, molybdenum ions and/or zirconium ions, each in the following preferred, particularly preferred and very particularly preferred concentration ranges ( Polymer calculated as pure polymer and metal ions calculated as corresponding metal). Mo 1 to 500 mg/l 10 to 250 mg/l 20 to 150 mg/l Cu 1 to 1000 mg/l 100 to 500 mg/l 150 to 225 mg/l Zr 20 to 500 mg/l 50 to 300 mg/l 50 to 150 mg/l cat. polymer 0.1 g/l to 3 g/l 0.3 g/l to 2 g/l 0.5 g/l to 1.5 g/l

The rinsing composition comprises - particularly if the metallic surface is aluminum or an aluminum alloy - preferably additionally 20 to 500 mg/l, more preferably 50 to 300 mg/l and particularly preferably 50 to 150 mg/l Ti, Zr and /or Hf in complexed form (calculated as metal). These are preferably fluoro complexes. In addition, the rinse composition preferably comprises 10 to 500 mg/l, more preferably 15 to 100 mg/l and particularly preferably 15 to 50 mg/l of free fluoride. The rinse composition particularly preferably contains Zr in complexed form (calculated as metal) and at least one type of metal ion selected from the group consisting of the ions of molybdenum, copper, silver, gold, palladium, tin and antimony, preferably molybdenum.

The pH of the rinse composition is preferably in the acidic range, more preferably in the range from 3 to 5, particularly preferably in the range from 3.5 to 5. Surprisingly, it was found that lowering the pH causes the deposition of molybdenum ions on the phosphate-coated metallic surface promotes. In the case of a rinsing solution containing molybdenum ions, the pH value is therefore preferably 3.5 to 4.5 and particularly preferably 3.5 to 4.0.

The rinse composition is essentially nickel-free. It preferably contains less than 0.1 g/l and particularly preferably less than 0.01 g/l nickel ions.

The rinsing composition preferably has a temperature in the range from 15 to 40 ° C. The metallic surface is treated with the rinsing composition preferably for 10 to 180, particularly preferably for 20 to 150 and very particularly preferably for 30 to 120 seconds, preferably by dipping or spraying.

An electrophoretic paint can then be deposited cathodically and a paint structure can be applied to the phosphate-coated metallic surface - as well as the metal surface that may have been treated with the rinsing composition.

If necessary, after treatment with the rinsing composition, the metallic surface is first rinsed, preferably with deionized water, and optionally dried.

The present disclosure further relates to the alkaline, aqueous, but unclaimed, cleaning composition described above, which contains at least one water-soluble silicate, as well as to the concentrate described at the relevant point from which this cleaning composition is available.

The disclosure also relates to an unclaimed phosphate-coated metallic surface, which is obtainable using the method according to the invention.

Finally, the invention also relates to the use of the method in the automotive sector, automotive suppliers or general industry.

The present invention will be explained below using exemplary embodiments and comparative examples that are not intended to be limiting.

Examples i) Production of cleaning and phosphating baths:

The following cleaning baths were prepared by mixing the components in demineralised water, adjusting the pH if necessary with phosphoric acid (cleaning bath A) and then diluting the mixture by a factor of 50 to 70: Cleansing bath A b C D E component Contents (g/l) Well water glass - 2.6 2.6 - 2.4 K-water glass - - - 3.1 - K-pyrophosphate 1 2 2 - - Na tripolyphosphate - - - 0.5 - K-tripolyphosphate - - - - 0.8 phosphoric acid - - - - 1.5 Phosphonic acid 0.1 - - - - Na-gluconate - - 0.4 - - Boric acid - - - - 2.0 Na nitrite - - 0.02 - - KOH (90%) 4.4 6 6 4.5 5.6 pH adjustment Yes no no no no PH value 10.5 11.6 11.6 11.2 11.3

The cleaning bath F and the cleaning bath G were also prepared. The cleaning bath F was identical to the cleaning bath B with the exception of the pH value of 10.5, while the cleaning bath G was identical to the cleaning bath E with the exception of the pH value of 10.5. The pH value for both cleaning baths F and G was adjusted with phosphoric acid.

By mixing the components in demineralised water (zinc, nickel and manganese are added as nitrates or phosphates) and adjusting the S value by lowering the free acid (FS) with sodium hydroxide solution, the following nickel-free phosphating baths were produced: Phosphating bath A' B' C' component Contents (g/l) Zn 1.3 1.3 1.3 Ni 1 0 0 Mn 1.0 1.0 1.5 Phosphate (calculated as P ₂ O ₅ ) 13 13.5 15 free fluoride 0.08 0.08 0.07 _BF4 ^- 1.0 1.0 1.0 nitrate 3 - 0.05 S value 0.08 0.06 0.07

The following rinsing bath was prepared by mixing H ₂ ZrF ₆ and ammonium heptamolybdate in demineralised water and adjusting the pH with dilute ammonia solution: component Contents (mg/l) Zr 130 Mo 50 PH value 4

ii) Treatment of test sheets:

Test sheets made of hot-dip galvanized steel (EA), electrolytically galvanized steel (G) and the aluminum alloy AA 6014 (AI) were immersed in one of the cleaning baths A to D for 300 seconds at 60 °C and then in an activation bath at 25 °C for 30 seconds , which contained 0.6 g/l zinc phosphate. The test panels were then immersed in one of the phosphating baths A' to C' for 180 seconds at 45 °C and then in the rinsing bath described above for 30 seconds at 25 °C. After thoroughly rinsing with demineralized water, the test panels were coated with a cathodic electrophoretic paint and a standard automotive paint composition (filler, base coat, clear coat).

iii) Corrosion protection and paint adhesion tests:

The test panels pretreated and painted in this way were then subjected to a cross-cut test in accordance with DIN EN ISO 2409. Three sheets were tested before and after exposure to condensation for 240 hours (DIN EN ISO 6270-2 CH).

The corresponding results (average values) can be found in Table 1. A cross-hatch result of 0 is the best, and one of 5 is the worst value. Values of 0 and 1 are comparably good values. <b>Table 1</b> (cf.-) Ex. Subst. Clean. Phosph. Cross-cut before stress after load VB1 E.A A A' 1.0 1.0 VB2 A B' 3.3 5.0 B1 C B' 1.0 3.0 B6 b C' 0.7 0.3 B7 F C' 0.7 0.7 B8 E C' 0.7 0.7 B9 G C' 0.3 1.7 VB3 G A A' 0.0 0.3 VB4 A B' 0.0 4.7 B2 C B' 0.3 0.7 VB5 Al A A' 0.0 0.0 VB6 A C' 0.0 0.0 B3 b C' 0.0 0.0

In addition, the test panels made of electrolytically and hot-dip galvanized steel were subjected to a VDA test (VDA 621-415; 10 rounds), whereby the paint infiltration (U) was determined in mm as well as the paint detachment after stone chipping (DIN EN ISO 20567-1, Author C) was determined. A result of 0 is the best, a result of 5 is the worst value after a rockfall. A value of up to 1.5 is considered a good value. The results (average values from three sheets) are also summarized in Table 2 . <b>Table 2</b> (cf.-) Ex. Subst. Clean. Phosph. VDA U (mm) Rockfall VB1 E.A A A' 0.3 0.5 VB2 A B' 3.0 1.5 B1 C B' 0.8 1.0 B4 b C' 1.1 nb B5 D C' 0.8 nb B6 b C' 0.9 1.5 B7 F C' 1.5 2.0 B8 E C' 2.1 1.5 B9 G C' 2.4 1.5 VB3 G A A' 0.6 0.7 VB4 A B' 2.4 2.8 B2 C B' 1.3 1.3

The aluminum alloy test panels, on the other hand, were subjected to a 240-hour CASS test according to DIN EN ISO 9227 and a filiform test according to DIN EN 3665. The results (average values from three sheets) are summarized in Table 3 . <b>Table 3</b> (cf.-) Ex. Subst. Clean. Phosph. CASS Filiform Medium Max. VB5 Al A A' 0.8 1.0 4.6 VB6 A C' 0.9 1.8 8.7 B3 b C' 0.5 0.9 6.9

iv) Results and discussion:

The cross-cut results in Table 1 clearly show the deterioration in paint adhesion with nickel-free compared to nickel-containing phosphating on hot-dip galvanized and electrolytically galvanized steel (see VB2 vs. VB1; VB4 vs. VB3).

By using a cleaning bath according to the invention, paint adhesion can be achieved with the nickel-free variant, which almost corresponds to that of the nickel-containing variant (see B1 vs. VB1 and B2 vs. VB3).

The same applies to the results in Table 2. Here too, the use of a cleaning bath according to the invention in nickel-free phosphating results in a significant improvement in the corrosion protection values. A further improvement results from the addition of gluconate and nitrite to the cleaning bath (see B1 vs. B4).

The CASS and Filiform results in Table 3 show that the use of a cleaning bath according to the invention in nickel-free phosphating on the aluminum alloy achieves a significant improvement in the corrosion protection values (cf. B3 vs. VB5 and VB6). In the case of CASS and Filiform, agent even better corrosion protection is achieved than with the nickel-containing variant.

From the comparison of examples B6 and B7 (see Table 1 and Table 2 ), the further improvement in the results achieved can be seen by choosing a pH value of 11.6 (B6) instead of a pH value of 10, 5 (B7).

From the comparison of examples B8 and B9 (see Table 1 and Table 2 ), the further improvement of the results achieved can be seen by choosing a pH value of 11.3 (B8) instead of a pH value of 10, 5 (B9).

Claims (10)

1. A method for phosphating of a metallic surface, which comprises treating a metallic surface one after the other with the following compositions:

   i) with an alkaline, aqueous cleaner composition which comprises at least one water-soluble silicate, where the at least one water-soluble silicate comprises at least one waterglass, and/or at least one metasilicate, where the at least one water-soluble silicate is present in a total concentration in the range from 0.01 to 15 g/l, which at 25°C has a water solubility in fully demineralized water of at least 1 mg/l, where the pH of the cleaner composition is in the range from 10.7 to 12.0, and then

   ii) with an acidic, aqueous phosphating composition which comprises zinc ions, manganese ions and phosphate ions and less than 0.01 g/l of nickel ions, where "phosphate ions" also refers to hydrogen phosphate, dihydrogen phosphate, phosphoric acid, pyrophosphoric acid and polyphosphoric acid and all of their partially and fully deprotonated forms, where the metallic surface already treated with the phosphating composition is further treated with an aqueous after-rinse composition which comprises molybdenum ions and zirconium ions.
2. The method according to claim 1 , wherein the pH of the cleaner composition is in the range from 11.0 to 12.0, preferably from 11.3 to 12.0 and more preferably in the range from 11.5 to 12.0.
3. The method according to claim 1 or 2, wherein the metallic surface is at least partly galvanized.
4. The method according to claim 1, wherein the at least one water-soluble silicate comprises at least one sodium waterglass and/or potassium waterglass.
5. The method according to any of the preceding claims, wherein the at least one water-soluble silicate is present in a total concentration preferably from 0.2 to 13 and more preferably from 0.5 to 10 g/l.
6. The method according to any of the preceding claims, wherein the cleaner composition comprises at least one phosphorus-containing complexing agent and/or at least one hydroxycarboxylic acid or salt thereof.
7. The method according to claim 6, wherein the at least one phosphorus-containing complexing agent comprises a pyrophosphate and/or tripolyphosphate.
8. The method according to claim 6 or 7, wherein the at least one hydroxycarboxylic acid or salt thereof comprises gluconate.
9. The method according to any of the preceding claims, wherein the cleaner composition comprises nitrite.
10. The use of the method according to any of the preceding claims in the sector of the automobile and automotive component supplier industry.