EP3676419A1 - Improved method for nickel-free phosphating metal surfaces - Google Patents

Abstract

The present invention relates to a process for the substantially nickel-free phosphating of a metallic surface in which a metallic surface is treated successively with the following compositions: i) with an alkaline, aqueous cleaning composition containing at least one water-soluble silicate and ii) with an acidic aqueous, substantially nickel-free phosphating composition comprising zinc ions, manganese ions and phosphate ions. The invention additionally relates to the above detergent composition itself and to a metallic surface which has been phosphate-coated by means of the above process and the use thereof.

Description

 Improved process for nickel-free phosphating of metallic

 surfaces

The present invention relates to a process for substantially nickel-free phosphating of a metallic surface using a specific detergent composition, this detergent composition itself and a process-phosphate-coated metallic surface and their use.

From the prior art phosphate coatings on metallic surfaces are known. Such coatings serve to protect the corrosion of the metallic surfaces and also as adhesion promoters for subsequent paint layers.

Such phosphate coatings are mainly used in the automotive industry and the general industry.

In addition to powder coatings and wet paints, the subsequent coating layers are above all cathodically deposited electrodeposition paints (KTL). Since during the deposition of KTL a current must flow between the metallic surface and the treatment bath, 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 by means of a nickel-containing phosphating solution. The elementary or as alloying constituent, e.g. Zn / Ni, deposited nickel ensures a suitable conductivity of the coating in the subsequent electrodeposition coating.

However, nickel ions are no longer desirable as part of treatment solutions because of their high toxicity and environmental toxicity, and should therefore be avoided or at least reduced in content as much as possible.

The use of nickel-free or low-nickel phosphating solutions is known in principle. However, this is limited to certain substrates such as steel.

Moreover, in the case of the above-mentioned nickel-poor or nickel-free systems, poor corrosion protection and paint adhesion values may result given KTL deposition conditions due to a non-optimal substrate surface. The object of the present invention was therefore to provide a method with which metallic surfaces can be phosphated essentially nickel-free, wherein the aforementioned disadvantages of the prior art are avoided.

This object is achieved by a method according to claim 1, a phosphating composition according to claim 12 and a phosphate-coated metallic surface according to claim 14.

In the method of the invention for essentially nickel-free phosphating of a metallic surface, a metallic surface is treated successively with the following compositions: i) with an alkaline aqueous cleaning composition containing at least one water-soluble silicate and then 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, on the other hand, but also an already conversion coated metallic surface can be treated by the method according to the invention. Whenever a "metallic surface" is mentioned below, an already conversion-coated metallic surface should therefore always be included as well, however, it is preferably an uncoated metallic surface.

For the purposes of the present invention, "aqueous composition" refers to a composition which contains water as solvent / dispersion medium at least in part, preferably for the most part, ie more than 50% by weight It may therefore be, for example, an emulsion, but it is preferably a solution, ie a composition which contains no coarsely dispersed constituents.

In the following, a "water-soluble silicate" is mentioned, a silicate is meant that at 25 ° C, a water solubility (in deionized water) of at least 1 mg / l, 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, even more preferably at least 100 g / l, more preferably at least 200 g / l, more preferably at least 300 g / l and more preferably at least 350 g / l. The silicate can also be present as a colloidal solution.

If a composition contains less than 0.3 g / l of nickel ions, it should be considered as "essentially nickel-free" for the purposes of the present invention. The phosphating composition preferably contains less than 0.1 g / l and more preferably less than 0.01 g / l 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 as well as all their partially and completely deprotonated forms should be included.

For the purposes of the present invention, "metal ion" is understood as meaning either a metal cation, a complex metal cation or a complex metal anion.

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

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

Before being treated with the acidic, aqueous, substantially nickel-free phosphating composition (step ii), the metallic surface is, according to the invention, first cleaned (step i), in particular degreased, in an alkaline, aqueous cleaning composition. If appropriate, an acidic or neutral pickling composition may also be used for this purpose. The detergent composition may be obtained from a concentrate by dilution with a suitable solvent, preferably with 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 detergent composition causes a better cleaning action and reduces the pickling attack in the cleaning bath (inhibiting effect).

The at least one water-soluble silicate in this case preferably comprises at least one water glass, in particular a lithium water glass, a soda water glass and / or a potassium silicate, more preferably a soda water glass and / or a potassium silicate, 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 silicate glass. The soda water glass is preferably one having a molar Na 2 O: SiO 2 ratio in the range from 1 to 4. The potassium silicate glass is likewise preferably one having a molar K 2 O: SiO 2 ratio in the range from 1 to 4 ,

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

The detergent composition may contain, in addition to the at least one water-soluble silicate, at least one cationic, nonionic and / or anionic surfactant and / or other additives, in particular complexing agents, oxidizing agents, oils and / or auxiliaries, e.g. Solvent, borate and / or carbonate included.

The addition of at least one complexing agent and / or at least one oxidizing agent has proved advantageous with regard to the corrosion protection and paint adhesion values achieved and is thus preferred.

In the detergent composition contained complexing agents cause a complexation of water hardness and dissolved cations, which by the pickling attack in the cleaner bath go into solution or present.

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

These are in particular phosphate-based complexing agents - preferably in turn condensed phosphates such as e.g. Pyrophosphates, tripolyphosphates and other polyphosphates - as well as phosphonic acids, e.g. 1-Hydroxyethane- (1, 1-diphosphonic acid) (HEDP) and its salts.

The phosphorus-containing, in particular the phosphate-based complexing agents are preferably in a total concentration in the range of 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. Very particular preference is given to gluconate. Such complexing agents are preferably present in a total concentration in the range of from 0.01 to 6 g / l, more preferably from 0.05 to 5 g / l, and most preferably from 0.1 to 4 g / l (calculated as sodium gluconate).

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. Very particularly preferred combinations are: i) tetrapotassium pyrophosphate and gluconate,

ii) pentasodium tripolyphosphate and gluconate. A preferred oxidizing agent is nitrite. The oxidizing agents are preferably in a total concentration in the range of 10 to 100 mg / l, more preferably from 20 to 50 mg / l (calculated as nitrite) before.

The cleaner composition is preferably added no iron ions, in particular no iron (III) ions. If necessary, iron ions present in the cleaning bath originate in this case exclusively from the treated metallic Surface.

To adjust the alkalinity of the cleaning composition, on the one hand, in particular, in particular, sodium hydroxide solution, potassium hydroxide solution, caustic soda or caustic potash, on the other hand, in particular phosphoric acid can be used. The pH of the cleaner composition is preferably in the range of 9.5 to 13, in particular in the range of 10.5 to 12, more preferably in the range of 10.7 to 12.0, more preferably of 1 1, 0 to 12, 0, more preferably from 1 1, 3 to 12.0 and particularly preferably in the range of 1 1, 5 to 12.0.

The detergent composition preferably has a temperature in the range of from 35 to 70, more preferably from 40 to 65, and most preferably from 45 to 60 ° C. The treatment of the metallic surface with the detergent composition is preferably carried out for 30 to 600, more preferably for 60 to 480 and most preferably for 90 to 360 seconds, preferably by means of dipping or spraying, or the combination of both. According to a preferred embodiment, the metallic surface is first sprayed with the detergent composition for 30 to 90 seconds and then immersed in it for 100 to 300 seconds.

After the cleaning / pickling and before the treatment of the metallic surface with the phosphating composition takes place advantageously at least one rinsing of the metallic surface with water, wherein the water optionally also dissolved in water additive such. As a nitrite or surfactant may be added.

Before treating the metallic surface with the phosphating composition, it is further advantageous to treat the metallic surface with an activating composition. The activation composition serves to deposit a plurality of ultrafine phosphate particles as seed crystals on the metallic surface. These help in the subsequent process step, in contact with the phosphating - preferably without interim rinsing - form a particular crystalline phosphate layer with the highest possible number of densely arranged fine phosphate crystals or a substantially closed phosphate layer. In particular, alkaline compositions based on titanium phosphate or zinc phosphate are suitable as activating compositions.

However, it may also be advantageous to add activating agents, in particular titanium phosphate or zinc phosphate, already to the cleaner composition, ie to carry out purification and activation in one step.

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

The phosphating composition may be obtained from a concentrate by dilution with a suitable solvent, preferably with 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:

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

The complex fluoride is preferably tetrafluoroborate (BF ₄ ^_ ) and / or hexafluorosilicate (SiF 6 ^{2 ~} ). Especially in the treatment of aluminum and / or galvanized material is a content of complex fluoride and single fluoride, such as sodium fluoride, in the phosphating advantageous.

Al ³⁺ is a bad poison in phosphating systems and can be removed from the system by complexation with fluoride, eg as cryolite. Complex fluorides become the bath fluoride also helps to improve paint adhesion and corrosion protection, and complex fluoride on galvanized material helps to prevent defects such as sticking ,

In particular, in the treatment of aluminum, it is also advantageous if the phosphating composition has a content of iron (III) ions. The iron (III) ions are preferably added to the phosphating composition. In this case, an addition amount of 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:

With regard to the nitroguanidine, however, a concentration in the range of 0.1 to 3.0 g / l has already been found to be advantageous with respect to the H2O2, a concentration in the range from 5 to 200 mg / l. Most preferably, the at least one accelerator is H2O2.

However, the phosphating composition preferably contains less than 1 g / l, more preferably less than 0.5 g / l, more preferably less than 0.2 g / l and most preferably less than 0.1 g / l of nitrate. Namely, especially in a galvanized surface, the nitrate in the phosphating causes an additional acceleration of Stratification reaction, which leads to lower coating weights but mainly reduces the incorporation of manganese in the crystal. However, if the manganese content of the phosphate coating is too low, this is at the expense of its alkali resistance.

Alkali resistance in turn plays a crucial role in subsequent cathodic electrodeposition. In this case, an electrolytic splitting of water occurs at the substrate surface: Hydroxide ions are formed. This causes the pH at the interface of the substrate to increase. It is true that only then can the electrocoating be agglomerated and separated. However, the increased pH can also damage the crystalline phosphate layer.

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

Furthermore, the phosphating composition can be characterized by the following preferred and particularly preferred parameter ranges:

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

Here "FS" stands for free acid, "FS (verd.)" 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 Phosphatierchemikalien and serves the ongoing monitoring of the working phosphating (see W. Rausch "The phosphating of metals", Eugen G. Leuze Verlag, 3rd edition, 2005, Chapter 8, p 332 ff.): Free acid (FS):

 (See W. Rausch "The Phosphatization 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 is 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, using a pH meter and an electrode, it is titrated with 0.1 M NaOH to a pH of 3.6. The amount of 0.1 M NaOH consumed in ml per 10 ml of the phosphating composition gives the value of the free acid (FS) in points.

Free acid (diluted) (FS (dil.)):

 (See W. Rausch "The Phosphatization 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 into a 300 ml Erlenmeyer flask. Subsequently, 150 ml of deionized water are added. Using a pH meter and an electrode, titrate with 0.1 M NaOH to a pH of 4.7. The consumed amount of 0.1 M NaOH in ml per 10 ml of the diluted phosphating composition gives the value of the free acid (diluted) (FS (dil.)) In points. About the difference to the free acid (FS) the content of complex fluoride can be determined. If this difference is multiplied by a factor of 0.36, the content of complex fluoride is SiF6 ^{2 ~} in g / l.

Total acid according to Fischer (GSF):

 (See W. Rausch "The Phosphatization of Metals", Eugen G. Leuze Verlag, 3rd Edition, 2005, Chapter 8.2, pp. 334-336)

Following determination of the free acid (diluted), the dilute phosphating composition is titrated to pH 8.9 after addition of potassium oxalate solution using a pH meter and electrode with 0.1 M NaOH. The consumption of 0.1 M NaOH in ml per 10 ml of the diluted phosphating composition hereby gives the total Fischer acid (GSF) in points. If this value is multiplied by 0.71, the total content of phosphate ions is calculated as P2O5. Total Acid (GS):

 (See W. Rausch "The Phosphatization 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 present as well as free and bound phosphoric acids (the latter being phosphates). It is determined by the consumption of 0.1 M NaOH using a pH meter and an electrode. For this purpose, 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 deionized water. It 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):

 (See 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 given by Divide the value of the free acid (FS) by the value of the total acid according to Fischer (GSF).

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

It has surprisingly been found that especially in the case of steel or hot dip galvanizing as a metallic surface, a temperature of the phosphating of less than 45 ° C, preferably in the range between 35 and 45 ° C leads to further improved corrosion and paint adhesion values. The treatment of the metallic surface with the phosphating composition is preferably carried out for 30 to 480, particularly preferably for 60 to 300 and very particularly preferably for 90 to 240 seconds, preferably by means of dipping or spraying.

By treating the metallic surface with the phosphating composition, depending on the surface being treated, the following preferred and particularly preferred zinc phosphate layer weights are disclosed in U.S. Pat metallic surface (determined by X-ray fluorescence analysis (RFA)):

Preferably, the metallic surface is rinsed after treatment with the phosphating composition, more preferably rinsed with demineralized water or city water.

Advantageously, the already treated with the phosphating, ie phosphate-coated, metallic surface is still treated with an aqueous Nachspülzusammensetzung. In this case, the metallic surface is optionally dried before treatment with the Nachspülzusammensetzung. The rinse-off composition can be obtained from a concentrate by dilution with a suitable solvent, preferably with water, by a factor between 1.5 and 1000, preferably between 5 and 700, and if necessary adding a pH modifying substance.

The treatment with the post-rinse composition makes it possible to adjust the electrical conductivity of the phosphate-coated metal surface in a targeted manner by producing defined pores in the phosphate layer. In this case, the conductivity may be either greater than, equal to, or smaller than that of a corresponding metal surface provided with a nickel-containing phosphate coating.

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

In one embodiment, the post-rinse composition contains at least one kind of metal ion selected from the group consisting of the ions of the following metals in the following preferred, most preferred and most preferred concentration ranges (all 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

Ag 1 to 500 mg / l 5 to 300 mg / l 20 to 150 mg / l

Au 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 post-rinse composition are deposited either in the form of a salt which preferably contains the corresponding metal cation (eg molybdenum or tin) 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 (eg copper, silver, gold or palladium).

In a preferred embodiment, the metal ions are molybdenum ions. These are preferably added as molybdate, more preferably as ammonium heptamolybdate and more preferably as ammonium heptamolybdate x 7 H2O to the post-rinse composition. The molybdenum ions can also be added as sodium molybdate.

However, molybdenum ions, for example, may also be added to the post-rinse composition in the form of at least one molybdenum cation-containing salt, 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 post-rinse composition itself contains a corresponding oxidizing agent.

More preferably, the post-rinse composition contains molybdenum ions in combination with copper ions, tin ions or zirconium ions.

It particularly preferably 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, polyethylenimines, polythiophenes and polypryrenes and mixtures and copolymers thereof and polyacrylic acid, wherein the content of molybdenum ions and zirconium ions is in each case in the range from 10 to 500 mg / l (calculated as metal) ,

The content of molybdenum ions 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 content of zirconium ions in the range from 50 to 300 mg / l, more preferably from 50 to 150 mg / l. According to a further preferred embodiment, the metal ions are copper ions. Preferably, the rinsing solution then contains these in a concentration of 100 to 500 mg / l, more preferably from 150 to 225 mg / l.

According to a further embodiment, the rinse-off composition according to the invention comprises at least one polymer selected from the group consisting of the polymer classes of the polyamines, polyethyleneamines, polyanilines, polyimines, polyethyleneimines, polythiophenes and polypryrenes and also their mixtures and copolymers.

The at least one polymer is preferably in a concentration in the range of 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).

The polymers used are preferably cationic polymers, in particular polyamines, polyethyleneamines, polyimines and / or polyethyleneimines. Particular preference is given to using a polyamine and / or polyimine, very particularly preferably a polyamine.

According to a third embodiment, the rinse-off composition according to the invention comprises at least one kind 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 polypryrenes and their Mixtures and copolymers, in each case 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).

According to a preferred embodiment, 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, in each case in the following preferred, particularly preferred and very particular preferred concentration ranges (polymer calculated as pure polymer and metal ions calculated as the corresponding metal).

The post-rinse composition comprises, in particular, when 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 of Ti, Zr and / or Hf in complexed form (calculated as metal). These are preferably fluoro complexes. In addition, the post-rinse composition preferably comprises 10 to 500 mg / l, more preferably 15 to 100 mg / l, and most preferably 15 to 50 mg / l of free fluoride. More preferably, the post-rinse composition contains Zr in complexed form (calculated as metal) and at least one kind of metal ions selected from the group consisting of the ions of molybdenum, copper, silver, gold, palladium, tin and antimony, preferably molybdenum. The pH of the post-rinse composition is preferably in the acidic range, more preferably in the range of 3 to 5, particularly preferably in the range of 3.5 to 5.

Surprisingly, it has been found that lowering the pH promotes the deposition of molybdenum ions on the phosphate-coated metallic surface. In a rinsing solution containing molybdenum ions, therefore, the pH is preferably 3.5 to 4.5, and more preferably 3.5 to 4.0.

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

The post-rinse composition preferably has a temperature in the range of 15 to 40 ° C. The treatment of the metallic surface with the post-rinse composition is preferably carried out for 10 to 180, particularly preferably for 20 to 150 and very particularly preferably for 30 to 120 seconds, preferably by means of dipping or spraying.

On the phosphate-coated - and optionally treated with the Nachspülzusammensetzung - metallic surface can then cathodically deposited an electrodeposition paint and a paint system can be applied.

Optionally, the metallic surface is first rinsed after the treatment with the Nachspülzusammensetzung, preferably with deionized water, and optionally dried. The present invention further relates to the alkaline aqueous cleaning composition described above, which contains at least one water-soluble silicate, as well as to the correspondingly described concentrate from which this cleaning composition is obtainable.

The invention additionally relates to a phosphate-coated metallic surface obtainable by the process according to the invention. Finally, the invention still relates to the use of the coated with the inventive method metallic surfaces in the field of automotive, automotive suppliers or general industry.

In the following, the present invention will be explained by non-limiting exemplary embodiments and comparative examples.

Examples i) Preparation of cleaning and phosphating baths:

 By mixing the components in demineralized water, optionally adjusting the pH with phosphoric acid (cleaning bath A) and then diluting the mixture by a factor of 50 to 70, the following cleaning baths were prepared:

In addition, the cleaning bath F and the cleaning bath G were also used. The cleaning bath F was identical to the cleaning bath B except for the pH of 10.5, while the cleaning bath G was identical to the cleaning bath E except for the pH of 10.5. The pH was adjusted both in the cleaning bath F and G with phosphoric acid.

By mixing the components in demineralized 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 prepared: phosphating

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 13 13.5 15

 (calculated as P2O5)

 free fluoride 0.08 0.08 0.07

BF ₄ - 1, 0 1, 0 1, 0

 Nitrate 3 - 0.05

 S-value 0.08 0.06 0.07

By mixing HZrFe and ammonium heptamolybdate in deionized water and adjusting the pH with dilute ammonia solution, the following rinse bath was prepared:

//) Treatment of test sheets:

Hot dip galvanized steel (EA), electrolytically galvanized steel (G) and aluminum alloy AA 6014 (AI) test plates were immersed in one of the cleaning baths A to D at 60 ° C for 300 seconds and then in an activating bath at 25 ° C for 30 seconds containing 0.6 g / l zinc phosphate. The test panels were then immersed for 180 seconds at 45 ° C in one of the phosphating baths A ^' to C and then for 30 seconds at 25 ° C in the rinse described above. After thorough rinsing with demineralized water, the test panels were also coated with a cathodic electrodeposition paint and a standard auto paint finish (filler, basecoat, clearcoat). iii) Corrosion and paint adhesion tests:

 The pretreated and painted test panels were then subjected to a cross-cut test in accordance with DIN EN ISO 2409. In each case, 3 panels 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 grating cut result of 0 is the best, and one of 5 the worst value. Values of 0 and 1 are comparable good values.

Table 1

In addition, the test plates made of electrolytically as well as hot-dip galvanized steel were subjected to a VDA test (VDA 621-415, 10 rounds), whereby the undercoat (U) was determined in mm and the lacquer removal after rockfall (DIN EN ISO 20567-1, Verf. C) was determined. A result of 0 is the best, one of 5 is the worst value after the fall of the stone. A value up to 1, 5 is to be regarded as a good value. The results (average values from three sheets) are also summarized in Tab. 2. Table 2

On the other hand, the aluminum alloy test plates were subjected to a 240-hour CASS test in accordance with DIN EN ISO 9227 and a filiform test in accordance with DIN EN 3665. The results (average values from three sheets) are summarized in Table 3.

Table 3

iv) Results and discussion:

The lattice cutting results of Table 1 clearly show the deterioration of the paint adhesion in nickel-free versus nickel-containing phosphating on hot-dip galvanized and electrolytically galvanized steel (compare VB2 vs. VB1, VB4 vs. VB3). By using a cleaning bath according to the invention, it is possible to achieve a paint adhesion in the nickel-free variant which almost corresponds to that of the nickel-containing variant (compare B1 vs. VB1 and B2 vs. VB3).

The same applies to the results of Table 2. Again, the use of a cleaning bath according to the invention in the nickel-free phosphating achieved a significant improvement in the corrosion protection values. A further improvement results from the addition of gluconate and nitrite to the cleaning bath (compare 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 (compare B3 vs. VB5 and VB6). In the case of CASS and Filiform, agent even a better corrosion protection than in the nickel-containing variant is achieved.

By comparing Examples B6 and B7 (see Table 1 and Table 2), the further improvement of the results obtained can be achieved by choosing a pH of 1 1, 6 (B6) instead of a pH of 10 , 5 (B7).

From the comparison of Examples B8 and B9 (see Table 1 and Tab. 2), the further improvement of the results achieved can be achieved by the choice of a pH of 1 1, 3 (B8) instead of a pH of 10 See 5 (B9).

Claims

claims 1 . Process for the essentially nickel-free phosphating of a metallic surface, characterized in that a metallic surface is treated successively with the following compositions:  i) with an alkaline, aqueous cleaning composition containing at least one water-soluble silicate and then  ii) with an acidic, aqueous, substantially nickel-free phosphating composition comprising zinc ions, manganese ions and phosphate ions. 2. The method according to claim 1, characterized in that the pH of the cleaner composition in the range of 10.7 to 12.0, preferably from 1 1, 0 to 12.0, more preferably from 1 1, 3 to 12.0 and more preferably in the range of 1 1, 5 to 12.0. 3. The method according to claim 1 or 2, characterized in that the metallic surface is at least partially galvanized. 4. The method according to any one of the preceding claims, characterized in that the at least one water-soluble silicate comprises at least one water glass, and / or at least one metasilicate. 5. The method according to claim 4, characterized in that the at least one water-soluble silicate comprises at least one soda water glass and / or potassium silicate. 6. The method according to any one of the preceding claims, characterized in that the at least one water-soluble silicate in a total concentration in the range of 0.01 to 15, preferably from 0.2 to 13 and particularly preferably from 0.5 to 10 g / l. 7. The method according to any one of the preceding claims, characterized in that the detergent composition comprises at least one phosphorus-containing complexing agent and / or at least one hydroxycarboxylic acid or its salt. 8. The method according to claim 7, characterized in that the at least a phosphorus-containing complexing agent comprises a pyrophosphate and / or tripolyphosphate. 9. The method according to claim 7 or 8, characterized in that the at least one hydroxycarboxylic acid or its salt comprises gluconate. 10. The method according to any one of the preceding claims, characterized in that the cleaner composition comprises nitrite. 1 1. Method according to one of the preceding claims, characterized in that the already treated with the phosphating composition metallic surface is treated with an aqueous Nachspülzusammensetzung comprising molybdenum ions and zirconium ions. 12. An alkaline, aqueous cleaner composition containing at least one water-soluble silicate according to any one of the preceding claims. 13. Concentrate from which a detergent composition according to claim 12 is obtainable by diluting with a suitable solvent and, if necessary, adding a pH-modifying substance. 14. A phosphate-coated metallic surface, characterized in that it is obtainable by the process according to any one of claims 1 to 11. 15. Use of the metallic surface according to claim 14 in the field of automotive, automotive suppliers or general industry.