Improved method for nickel-free phosphating metal surfaces

Abstract

The present invention relates to a process for the substantially nickel-free phosphating of a metal surface in which the metal surface is treated sequentially with i) an alkaline aqueous detergent composition comprising at least one water-soluble silicate, and ii) an acidic aqueous and substantially nickel-free phosphating composition comprising zinc ions, manganese ions and phosphate ions. The invention also relates to the above cleaning agent composition itself, and to metal surfaces coated with phosphate by the above method and to the use thereof.

Description

[0001] The present application is a divisional application of patent application no. 201880056072.4, filed on August 28, 2018, having the title "Improved process for nickel-free phosphating of metal surfaces".

[0002] The present invention relates to a process for the essentially nickel-free phosphating of metal surfaces using a specific cleaner composition, the cleaner composition as such and the phosphate-coated metal surface by the process and the use of said surface.

[0003] From the prior art, phosphate coatings on metal surfaces are known. Such coatings serve to protect the metal surface from corrosion and, in addition, as adhesion promoters for subsequent film coatings.

[0004] Such phosphate coatings are used, inter alia, in the automotive industry and in general industrial sectors.

[0005] The subsequent film coatings and powder coatings and wet lacquers are, inter alia, cathodically deposited electrocoat (CEC) materials. Since the deposition of CECs requires a current flow between the metal surface and the treatment bath, it is important to set a defined electrical conductivity in the phosphate coating to ensure an effective and uniform deposition.

[0006] Therefore, phosphating solutions containing nickel are generally used to apply phosphate coatings. The nickel (elemental or alloy component, e.g. in the form of Zn / Ni) deposited in this process provides the appropriate electrical conductivity of the coating during the subsequent electrocoating procedure.

[0007] However, due to the high toxicity and environmental harmfulness of nickel ions, nickel ions are no longer an ideal component of the treatment solution and, therefore, should be avoided as much as possible or at least reduced in quantity.

[0008] In principle, it is indeed known to use nickel-free or low-nickel phosphating solutions. However, this is limited to specific substrates, such as steel.

[0009] In addition, due to the non-ideal substrate surface, the nickel-free or low-nickel systems can lead to poor anticorrosion values and coating adhesion values under the prevailing CEC deposition conditions.

[0010] It was therefore an object of the present invention to provide a process with which a metal surface can be subjected to an essentially nickel-free phosphating, in which the disadvantages of the prior art described above are avoided.

[0011] This object is achieved by the process according to claim 1, the phosphating composition according to claim 12 and the phosphate-coated metal surface according to claim 14.

[0012] By the inventive process for the essentially nickel-free phosphating of metal surfaces, the metal surface is successively treated with the following compositions:

[0013] i) an aqueous alkaline cleaner composition comprising at least one water-soluble silicate, and then ii) an aqueous acidic substantially nickel-free phosphating composition comprising zinc ions, manganese ions and phosphate ions.

[0014] Definitions:

[0015] The process according to the application can be used for treating uncoated metal surfaces or already conversion-coated metal surfaces. Thus, in the following reference to "metal surfaces" always also includes already conversion-coated metal surfaces. However, it is preferred that the metal surfaces are uncoated.

[0016] For the purposes of the present application, "aqueous composition" is a composition which comprises water at least partially, preferably predominantly, i.e. to an extent of more than 50% by weight, as its solvent / dispersion medium. In addition to dissolved components, it can also comprise coarsely dispersed components. Thus, it can be, for example, an emulsion. Preferably, however, it is a solution, in other words a composition which does not contain coarsely dispersed components.

[0017] Reference to "water-soluble silicate" in the following means a silicate which has a water solubility (in fully demineralised water) at 25°C 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, more preferably at least 100 g / l, more preferably at least 200 g / l, more preferably at least 300 g / l, very preferably at least 350 g / l. The silicate can also be in the form of a colloidal solution.

[0018] When the composition comprises less than 0.3 g / l of nickel ions, it is considered to be "substantially nickel-free" for the purposes of the present application. The phosphating composition preferably comprises less than 0.1 g / l, more preferably less than 0.01 g / l of nickel ions.

[0019] For the purposes of the present application, "phosphate ions" also means hydrogen phosphate, dihydrogen phosphate and phosphoric acid. In addition, it is intended to include pyrophosphoric acid and polyphosphoric acid and all partial and fully deprotonated forms thereof.

[0020] For the purposes of the present application, "metal ions" alternatively are metal cations, complexed metal cations or complexed metal anions.

[0021] The metal surfaces preferably include steel, steel alloys, hot-dip galvanizing systems, electrolytic galvanizing systems, zinc alloys such as Zn / Fe or Zn / Mg, aluminium or aluminium alloys. In the case of hot-dip galvanizing and electrolytic galvanizing systems, these are in each case more particularly such systems on steel. The metal surfaces are more particularly at least partially galvanized.

[0022] The process according to the application is particularly suitable for multi-metal applications, in particular for metal surfaces, in particular zinc-plated systems, preferably hot-dip galvanized systems and electrolytic galvanized systems, comprising aluminum and / or aluminum alloys, preferably aluminum alloys.

[0023] Before the treatment (step ii) with the acidic aqueous and substantially nickel-free phosphating composition, the metal surface according to the application is first cleaned (step i), and more particularly degreased, in an alkaline aqueous cleaner composition. For this purpose, optionally, an acidic or neutral pickling composition can also be used additionally.

[0024] In this case, the cleaner composition can be obtained from a concentrate by dilution with a suitable solvent, preferably water, preferably with 1.5 to 1000, more preferably 50 to 200, times, and if necessary, by addition of pH-adjusting substances.

[0025] The at least one water-soluble silicate in the cleaner composition serves to improve the cleaning effect and to reduce pickling attack in the cleaning bath (inhibiting effect).

[0026] Here, the at least one water-soluble silicate preferably comprises at least one water glass, more particularly lithium water glass, sodium water glass and / or potassium water glass, more preferably sodium water glass and / or potassium water glass, and / or at least one metasilicate, such as sodium metasilicate (Na2SiO3).

[0027] It is particularly preferred that the at least one water-soluble silicate comprises sodium water glass or potassium water glass.

[0028] The sodium water glass is preferably a sodium water glass having a molar ratio Na2O:SiO2 of 1 to 4. The potassium water glass is likewise preferably a potassium water glass having a molar ratio K2O:SiO2 of 1 to 4.

[0029] The at least one water-soluble silicate is preferably present in a total concentration of 0.01 to 15 g / l, more preferably 0.2 to 13 g / l, very preferably 0.5 to 10 g / l.

[0030] In addition to the at least one water-soluble silicate, the cleaner composition can also comprise at least one cationic, nonionic and / or anionic surfactant and / or other additives, in particular complexing agents, oxidizing agents, oils and / or auxiliaries such as solubilizers, borates and / or carbonates.

[0031] The addition of at least one complexing agent and / or at least one oxidizing agent has proven to be advantageous and is therefore preferred in terms of the corrosion protection and coating adhesion values achieved.

[0032] The complexing agent serves in the cleaner composition to cause complexing of water hardness and dissolved cations, which are present in the solution as a result of pickling attack or enter the solution in the cleaner bath.

[0033] Preferred complexing agents here are on the one hand phosphorus-containing complexing agents.

[0034] These are more particularly phosphonate-based complexing agents - again preferably condensed phosphates such as pyrophosphates, tripolyphosphates and other polyphosphates, and phosphonic acids such as 1-hydroxyethane-(1,1 -diphosphonic acid) (HEDP) and salts thereof.

[0035] The phosphorus-containing, in particular phosphonate-based, complexing agents are present in a total concentration of preferably 0.01 to 15 g / l, more preferably 0.05 to 13 g / l, very preferably 0.1 to 10 g / l (calculated as tetrapotassium pyrophosphate).

[0036] On the other hand, preferred complexing agents are hydroxycarboxylic acids having at least one hydroxyl group and at least one carboxyl group and salts thereof, in particular sugar acids and salts thereof, more preferably gluconate and heptonate. Very particular preference is given to gluconate. Such complexing agents are preferably present in a total concentration of 0.01 to 6 g / l, more preferably 0.05 to 5 g / l, very preferably 0.1 to 4 g / l (calculated as sodium gluconate).

[0037] According to a particularly preferred embodiment, the cleaner composition comprises at least one phosphorus-containing complexing agent, more particularly pyrophosphate and / or tripolyphosphate, and at least one hydroxycarboxylic acid or salt thereof, more particularly gluconate. Particularly preferred combinations here are as follows:

[0038] i) tetrapotassium pyrophosphate and gluconate,

[0039] ii) pentasodium tripolyphosphate and gluconate.

[0040] A preferred oxidizing agent is nitrite. The oxidizing agent is preferably present in a total concentration of 10 to 100 mg / l, more preferably 20 to 50 mg / l (calculated as nitrite).

[0041] It is preferred not to add iron ions, more particularly iron(III) ions, to the cleaner composition. In this case, any iron ions present in the cleaning bath originate solely from the metal surface being treated.

[0042] In order to adjust the alkalinity of the cleaner composition, on the one hand sodium hydroxide, potassium hydroxide, caustic soda or caustic potash can be used in particular, and on the other hand phosphoric acid can be used in particular.

[0043] In this case, the pH of the cleaner composition is preferably 9.5 to 13, more particularly 10.5 to 12, more preferably 10.7 to 12.0, more preferably 11.0 to 12.0, more preferably 11.3 to 12.0, very preferably 11.5 to 12.0.

[0044] The temperature of the cleaner composition is preferably 35 to 70°C, more preferably 40 to 65°C, very preferably 45 to 60°C. The metal surface is treated with the cleaner composition preferably for 30 to 600 seconds, more preferably for 60 to 480 seconds, very preferably for 90 to 360 seconds (preferably by immersion or spraying or a combination of both).

[0045] According to one preferred embodiment, the metal surface is first sprayed with the cleaner composition for 30 to 90 seconds and then immersed therein for 100 to 300 seconds.

[0046] After the cleaning / pickling and before the metal surface is treated with the phosphating composition, it is also advantageous to rinse the metal surface at least with water, in which case the water can also optionally have been mixed with water-soluble additives such as nitrite or surfactants.

[0047] Furthermore, before the metal surface is treated with the phosphating composition, it is advantageous to additionally treat the metal surface with an activation composition. The purpose of the activation composition is to deposit a large number of ultrafine phosphate particles on the metal surface as seed crystals. These crystals help to form a phosphate layer, more particularly a crystalline phosphate layer (which has a very large number of finely set fine phosphate crystals) or a substantially non-porous phosphate layer, when the metal surface is contacted with the phosphating composition in a subsequent process step, preferably without the need for rinsing in between.

[0048] Activation compositions which are desirable in this case include, inter alia, alkaline compositions based on titanium phosphate or zinc phosphate.

[0049] However, it can also be advantageous to add an activation agent, in particular titanium phosphate or zinc phosphate, to the cleaner composition itself, in other words to carry out the cleaning and the activation in one step.

[0050] The acidic aqueous and substantially nickel-free phosphating composition comprises zinc ions, manganese ions and phosphate ions.

[0051] Here, the phosphating composition can be obtained from a concentrate by dilution with 1.5 to 100-fold, preferably 5 to 50-fold, of a suitable solvent, preferably water, and, if necessary, by addition of a pH-adjusting substance.

[0052] The phosphating composition preferably comprises the following components in the following preferred and more preferred concentration ranges:

[0053] Zn 0.3-3.0g / l 0.5-2.0g / l Mn 0.3-2.0g / l 0.5-1.5g / l phosphate (as P2O5) 8-25g / l 10-18g / l free fluoride 30-250 mg / l 50-180 mg / l complex fluoride (e.g. SiF6 2- and / or BF4 - counted) 0-5g / l 0.5-3g / l

[0054] However, it has proven advantageous for the concentration with respect to manganese ions to be 0.3 to 2.5 g / l and for the concentration with respect to free fluoride to be 10 to 250 mg / l.

[0055] The complexing fluoride is preferably tetrafluoroborate (BF4 - ) and / or hexafluorosilicate (SiF6 2-).

[0056] In particular in the treatment of aluminum and / or galvanized materials, it is advantageous for complex fluoride as well as simple fluoride, such as sodium fluoride, to be present in the phosphating composition.

[0057] Al in phosphating systems 3+ is a bath poison and can be removed from the system by complexing with fluoride (e.g. in the form of cryolite). The complex fluoride is added to the bath as "fluoride buffer", since otherwise the fluoride content would quickly drop and coating would no longer take place. The fluoride then supports the formation of the phosphate layer and thus also indirectly leads to an improvement in the adhesion and corrosion resistance of the coating. Furthermore, on galvanized materials, the complex fluoride helps to prevent defects such as mottling.

[0058] Furthermore, it is advantageous, especially in the case of the treatment of aluminum, for the phosphating composition to contain iron (III) ions. The iron (III) ions are preferably added to the phosphating composition. In this case, the amount of iron (III) ions added is preferably 0.001 to 0.2 g / l, more preferably 0.001 to 0.1 g / l, more preferably 0.005 to 0.1 g / l, very preferably 0.005 to 0.05 g / l, especially preferably 0.005 to 0.02 g / l.

[0059] The phosphating composition further preferably comprises at least one accelerator selected from the following compounds in the following preferred and more preferred concentration ranges:

[0060] nitroguanidine 0.2-3.0g / l 0.2-1.55g / l H2O2 10-100 mg / l 15-50 mg / l Nitroguanidine / H2O2 0.2-2.0 g / l 10-50 mg / l 0.2-1.5 g / l 15-30 mg / l nitrite 30-300 mg / l 90-150 mg / l hydroxylamine 0.1-5g / l 0.4-3g / l

[0061] However, it has proved advantageous for the concentration to be 0.1 to 3.0 g / l in the case of nitroguanidine and 5 to 200 mg / l in the case of H2O2.

[0062] Very preferably, the at least one accelerator is H2O2.

[0063] However, the phosphating composition preferably comprises less than 1 g / l, more preferably less than 0.5 g / l, very preferably less than 0.2 g / l, especially preferably less than 0.1 g / l of nitrate.

[0064] This is because, in the case of galvanized surfaces, the nitrate in the phosphating composition leads, inter alia, to an additional acceleration of the coating formation reaction, resulting in a reduction in the coating weight and, inter alia, a reduction in the manganese incorporation into the crystal. However, if the manganese content of the phosphate coating is too low, its resistance to alkalis becomes poor.

[0065] Alkaline resistance is also crucial in the subsequent cathodic electrodeposition of the coating. In this process, water is ionized at the surface of the substrate: hydroxide ions are formed. As a result, the pH at the interface of the substrate is increased. In fact, only in this way can the electrodeposition material be agglomerated and deposited. However, the increased pH can also damage the crystalline phosphate layer.

[0066] The temperature of the phosphating composition is preferably 30-55°C.

[0067] Furthermore, the phosphating composition can be characterized by the following preferred and more preferred parameter ranges:

[0068] FA 0.3-2.0 0.7-1.6 FA (diluted) 0.5-8 1-6 TAF 12-28 22-26 TA 12-45 18-35 A value 0.01-0.2 0.03-0.15 temperature 30-50℃ 35-45℃

[0069] However, it has proven advantageous for the value in terms of the FA parameter to be 0.2-2.5 and for the value in terms of the temperature to be 30-55°C.

[0070] In this list, "FA" stands for free acid, "FA (diluted)" stands for free acid (diluted), "TAF" stands for total acid (Fischer), "TA" stands for total acid and "A value" stands for acid value.

[0071] These parameters are determined as part of the analytical examination of the phosphating chemicals and are used for the continuous monitoring of the working phosphating bath (cf. W. Rausch "Die Phosphatierung von Metallen", Eugen G. Leuze Verlag, 3rd edition, 2005, Chapter 8, page 332 and following pages):

[0072] Free acid (FA):

[0073] (cf. W. Rausch "Die Phosphatierung von Metallen", Eugen G. Leuze Verlag, 3rd edition, 2005, Section 8.1, pages 333-334)

[0074] To determine the free acid, 10 ml of the phosphating composition are pipetted into a suitable container, such as a 300 ml conical flask. If the phosphating composition contains complexing fluoride, an additional 2-3 g of potassium chloride is added to the sample. The pH meter and electrode are then used to titrate with 0.1 M NaOH to a pH of 3.6. The amount of 0.1 M NaOH consumed in this titration, in millilitres per 10 millilitres of phosphating composition, gives the value for the free acid (FA) in points.

[0075] Free acid (diluted) (FA (diluted)):

[0076] (see W. Rausch "Die Phosphatierung von Metallen", Eugen G. Leuze Verlag, 3rd edition, 2005, section 8.1, pages 333-334)

[0077] To determine free acid (diluted), 10 ml of phosphating composition are pipetted into a suitable container, such as a 300 ml conical flask. Then 150 ml of completely demineralised water are added. Using a pH meter and electrode, titrate with 0.1 M NaOH to pH 4.7. The amount of 0.1 M NaOH consumed in this titration (in ml per 10 ml of diluted phosphating composition) gives the value for free acid (diluted) (FA (diluted)) in points. The amount of complexed fluoride can be determined from the difference to free acid (FA). If this difference is multiplied by the factor 0.36, the result is the amount of complexed fluoride, such as SiF6 2- , in g / l.

[0078] Total acid (Fischer) (TAF):

[0079] (see W. Rausch "Die Phosphatierung von Metallen", Eugen G. Leuze Verlag, 3rd edition, 2005, section 8.2, pages 334-336)

[0080] After determining free acid (diluted), the diluted phosphating composition is titrated with 0.1 M NaOH to pH 8.9 using a pH meter and electrode after addition of potassium oxalate solution. The amount of 0.1 M NaOH consumed in this procedure (in ml per 10 ml of diluted phosphating composition) gives the total acid (Fischer) (TAF) in points. If this value is multiplied by 0.71, the result is the total amount of phosphate ions (in P2O5).

[0081] Total acid (TA):

[0082] (see W. Rausch "Die Phosphatierung von Metallen", Eugen G. Leuze Verlag, 3rd edition, 2005, section 8.3, pages 336-338)

[0083] Total acid (TA) is the sum of the divalent cations present and the free and bound phosphoric acid (the latter being phosphates). It is determined by 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 container, such as a 300 ml conical flask, and diluted with 25 ml of completely demineralised water. Subsequently, titration is carried out with 0.1 M NaOH to pH 9. The consumption in this procedure (in ml per 10 ml of diluted phosphating composition) corresponds to the point number of the total acid (TA).

[0084] Acid value (A value):

[0085] (see W. Rausch "Die Phosphatierung von Metallen", Eugen G. Leuze Verlag, 3rd edition, 2005, section 8.4, page 338)

[0086] The acid value (A value) represents the ratio FA : TAF and is obtained by dividing the value of the free acid (FA) by the value of the total acid (Fisher) (TAF).

[0087] Further improvement of the coating adhesion is surprising due to the acid value being set to 0.03 - 0.065, more particularly 0.04 - 0.06, especially on hot-dip galvanised surfaces.

[0088] Surprisingly, it was found that a phosphating composition temperature of less than 45°C, preferably 35 - 45°C, leads to further improved corrosion and coating adhesion values, especially in the case of steel or hot-dip galvanised systems as metal surfaces.

[0089] The metal surface is treated with the phosphating composition preferably for 30 - 480 seconds, more preferably for 60 - 300 seconds, very preferably for 90 - 240 seconds (preferably by immersion or spraying).

[0090] Depending on the surface treated, the treatment of the metal surface with the phosphating composition leads to the following preferred and more preferred zinc phosphate coating weights (determined by X-ray fluorescence analysis (XRF)) on the metal surface:

[0091]

[0092]

[0093] After treatment with the phosphating composition, the metal surface is preferably rinsed, more preferably rinsed with completely demineralised water or municipal water.

[0094] It is advantageous to further treat the metal surface which has been treated with the phosphating composition and is thus coated with phosphates with an aqueous after-rinse composition. In this case, the metal surface is optionally dried before treatment with the after-rinse composition.

[0095] Here, the post-rinse composition can be obtained from a concentrate by dilution with 1.5 to 1000-fold, preferably 5 to 700-fold, of a suitable solvent, preferably water, and, if necessary, the addition of pH-adjusting substances.

[0096] The treatment with the post-rinse composition allows the conductivity of the phosphate-coated metal surface to be adjusted in a targeted manner by producing defined pores in the phosphate layer. In this case, the conductivity can be greater than, equal to, or less than the conductivity of the corresponding metal surface provided with a nickel-containing phosphate coating.

[0097] Here, the adjusted conductivity of the phosphate-coated metal surface can be influenced by the varying concentration of the given metal ions and / or polymers in the post-rinse composition.

[0098] According to one embodiment, the post-rinse composition comprises metal ions of at least one metal selected from the following (each in the respective metal):

[0099] Mo 1-500 mg / l 10-250 mg / l 20-150 mg / l Cu 1-1000 mg / l 100-500 mg / l 150-225 mg / l Ag 1-500 mg / l 5-300 mg / l 20-150 mg / l Au 1-500 mg / l 10-300 mg / l 20-200 mg / l Pd 1-200 mg / l 5-100 mg / l 15-60 mg / l Sn 1-500 mg / l 2-200 mg / l 3-100 mg / l Sb 1-500 mg / l 2-200 mg / l 3-100 mg / l Ti 20-500 mg / l 50-300 mg / l 50-150 mg / l Zr 20-500 mg / l 50-300 mg / l 50-150 mg / l Hf 20-500 mg / l 50-300 mg / l 50-150 mg / l

[0100] The metal ions comprised in the post-rinse composition are deposited on the surface to be treated (for example copper, silver, gold or palladium) in the form of a salt which comprises the respective metal cation (for example molybdenum or tin), preferably in at least two oxidation states, more particularly hydroxyl oxide, hydroxide, spinel or defect spinel, or in the form of the respective metal cation (for example molybdenum or tin) in elemental form.

[0101] According to one preferred embodiment, the metal ions are molybdenum ions. They are preferably added to the post-rinse composition in the form of a molybdate, more preferably ammonium heptamolybdate, very preferably ammonium heptamolybdate x 7 H2O. The molybdenum ions can also be added in the form of sodium molybdate.

[0102] The molybdenum ions can alternatively be added to the post-rinse composition, for example, in the form of at least one salt which comprises the molybdenum cation, for example molybdenum chloride, and then oxidized to a molybdate by a suitable oxidizing agent, examples of which are the accelerators described earlier above. In this case, the post-rinse composition itself comprises the respective oxidizing agent.

[0103] It is further preferred that the post-rinse composition comprises molybdenum ions in combination with copper ions, tin ions or zirconium ions.

[0104] It is particularly preferred that it comprises molybdenum ions in combination with zirconium ions and optionally also comprises a polymer or copolymer more particularly selected from the following polymer classes: polyamines, polyvinylamines, polyanilines, polyimines, polyethyleneimines, polythiophenes and polypyrroles, mixtures thereof and copolymers thereof, and polyacrylic acids, with the content of molybdenum ions and zirconium ions in each case being 10 to 500 mg / l (in the metal).

[0105] Herein, the content of molybdenum ions is preferably 20 to 150 mg / l, more preferably 25 to 100 mg / l, very preferably 30 to 75 mg / l, and the content of zirconium ions is preferably 50 to 300 mg / l, more preferably 50 to 150 mg / l.

[0106] According to a further preferred embodiment, the metal ions are copper ions. In this case, they are preferably present in the after-rinse solution in a concentration of 100 to 500 mg / l, more preferably 150 to 225 mg / l.

[0107] According to a further embodiment, the after-rinse composition according to the application comprises at least one polymer selected from the following polymer classes: polyamines, polyvinylamines, polyanilines, polyimines, polyethyleneimines, polythiophenes and polypyrroles, and mixtures thereof and copolymers thereof.

[0108] Herein, the concentration of the at least one polymer comprised is preferably 0.1 to 5 g / l, more preferably 0.1 to 3 g / l, more preferably 0.3 to 2 g / l, very preferably 0.5 to 1.5 g / l (based on pure polymer).

[0109] The polymer used is preferably a cationic polymer, in particular a polyamine, a polyvinylamine, a polyimine and / or a polyethyleneimine. It is particularly preferred to use a polyamine and / or a polyimine, very preferably a polyamine.

[0110] According to a third embodiment, the after-rinse composition according to the application comprises in each case at least one metal ion selected from the following: molybdenum, copper, silver, gold, palladium, tin, antimony, titanium, zirconium and hafnium, and at least one polymer selected from the following polymer classes: polyamines, polyvinylamines, polyanilines, polyimines, polyethyleneimines, polythiophenes and polypyrroles, and mixtures thereof and copolymers thereof, in the following preferred, more preferred and very preferred concentration ranges (polymer based on pure polymer and metal ion based on the respective metal).

[0111] Mo 1-500 mg / l 10-250 mg / l 20-150 mg / l Cu 1-1000 mg / l 100-500 mg / l 150-225 mg / l Ag 1-500 mg / l 5-300 mg / l 20-150 mg / l Au 1-500 mg / l 10-300 mg / l 20-200 mg / l Pd 1-200 mg / l 5-100 mg / l 15-60 mg / l Sn 1-500 mg / l 2-200 mg / l 3-100 mg / l Sb 1-500 mg / l 2-200 mg / l 3-100 mg / l Ti 20-500 mg / l 50-300 mg / l 50-150 mg / l Zr 20-500 mg / l 50-300 mg / l 50-150 mg / l Hf 20-500 mg / l 50-300 mg / l 50-150 mg / l polymer 0.1-3g / l 0.3-2g / l 0.5-1.5g / l

[0112] According to a preferred embodiment, the at least one polymer is a cationic polymer, more particularly a polyamine and / or a polyimine, and the metal ions are copper ions, molybdenum ions and / or zirconium ions, in each case in the preferred, more preferred and very preferred concentration ranges (polymer based on pure polymer and metal ion based on the respective metal).

[0113] Mo 1-500 mg / l 10-250 mg / l 20-150 mg / l Cu 1-1000 mg / l 100-500 mg / l 150-225 mg / l Zr 20-500 mg / l 50-300 mg / l 50-150 mg / l cationic polymer 0.1-3g / l 0.3-2g / l 0.5-1.5g / l

[0114] In particular if the metal surface is aluminum or an aluminum alloy, the post rinse composition preferably further comprises 20 to 500 mg / l, more preferably 50 to 300 mg / l, very preferably 50 to 150 mg / l of Ti, Zr and / or Hf in complex form (as metal). The complex is preferably a fluoro complex. Furthermore, the post rinse composition preferably comprises 10 to 500 mg / l, more preferably 15 to 100 mg / l, very preferably 15 to 50 mg / l of free fluoride.

[0115] It is particularly preferred that the post rinse composition comprises Zr in complex form (as metal) and at least one metal ion selected from the group consisting of molybdenum, copper, silver, gold, palladium, tin and antimony, preferably molybdenum.

[0116] The pH of the post rinse composition is preferably in the acidic range, more preferably 3 to 5, very preferably 3.5 to 5.

[0117] Surprisingly it was found that a reduction of the pH value promotes the deposition of molybdenum ions on the phosphate coated metal surface. Thus, in case the post rinse solution comprises molybdenum ions, the pH is preferably 3.5 to 4.5, more preferably 3.5 to 4.0.

[0118] The post rinse composition is essentially nickel free. It preferably comprises less than 0.1 g / l, more preferably less than 0.01 g / l of nickel ions.

[0119] The temperature of the post rinse composition is preferably 15 to 40°C. The treatment of the metal surface with the post rinse composition is preferably for 10 to 180 seconds, more preferably for 20 to 150 seconds, very preferably for 30 to 120 seconds (preferably by dipping or spraying).

[0120] Then, an electrocoat material can be cathodically deposited on the phosphate coated metal surface - which is optionally further treated with the post rinse composition - and the coating system is applied.

[0121] In this case, after the treatment with the post rinse composition, the metal surface is optionally first rinsed, preferably with fully demineralized water, and optionally dried.

[0122] The present invention additionally relates to the above described alkaline aqueous cleaner composition comprising at least one water soluble silicate and the concentrate described at the respective point from which the cleaner composition is obtainable.

[0123] Furthermore, the present invention relates to a phosphate coated metal surface obtainable by the inventive method.

[0124] Finally, the present invention also relates to the use of the metal surface coated with the inventive method in the automotive, automotive parts supplier or general industry sector.

[0125] In the following, the application is intended to be illustrated by working examples, which are to be understood as not imposing limitations, and by comparative examples. Examples

[0126] i) Preparation of cleaning and phosphating baths:

[0127] The components were mixed in fully demineralized water, optionally the pH was adjusted with phosphoric acid (cleaning bath A), and then the mixture was diluted 50-70 times to prepare the following cleaning baths:

[0128]

[0129]

[0130] Additionally, cleaning bath F and cleaning bath G were prepared. Cleaning bath F is identical to cleaning bath B except that the pH is 10.5, while cleaning bath G is identical to cleaning bath E except that the pH is 10.5. In the case of cleaning bath F and cleaning bath G, the pH was adjusted using phosphoric acid.

[0131] The components were mixed in fully demineralized water (zinc, nickel and manganese were added in the form of nitrates and / or phosphates) and the A value was adjusted by lowering the free acid (FA) with sodium hydroxide to prepare the following nickel-free phosphating bath:

[0132]

[0133]

[0134] H2ZrF6and ammonium heptamolybdate were mixed in fully demineralized water and the pH was adjusted using dilute aqueous ammonia to prepare the following post rinse bath:

[0135] component amount (mg / l) Zr 130 Mo 50 pH 4

[0136] ii) Treatment of test panels:

[0137] Test panels of hot dip galvanized steel (EA), electrolytic galvanized steel (G) and aluminum alloy AA 6014 (Al) were immersed in one of the cleaning baths A-D at 60°C for 300 seconds, followed by immersion in an activation bath containing 0.6 g / l zinc phosphate at 25°C for 30 seconds. The test panels were then immersed in one of the phosphating baths A'-C' at 45°C for 180 seconds, followed by immersion in the post rinse bath described above at 25°C for 30 seconds. After thorough rinsing with fully demineralized water, the test panels were further coated with cathodic electrocoating and a standard automotive coating system (filler, basecoat, clearcoat).

[0138] iii) Corrosion protection and coating adhesion tests:

[0139] The test panels thus pretreated and coated in this way were subsequently subjected to the DIN EN ISO 2409 scribe test. In each case, 3 panels were tested before and after exposure to condensed water for 240 hours (DIN EN ISO 6270-2 CH). The respective results (average values) are to be found in Table 1. In these results, a scribe result of 0 is the best, with a result of 5 being the worst result. Here, results of 0 and 1 have a comparable quality.

[0140] Table 1

[0141]

[0142]

[0143] In addition, test panels of electrogalvanized and hot-dip galvanized steel were subjected to the VDA test (VDA 621-415; 10 rounds), which determines the film reduction (U) in mm and the film separation after chipping (DIN EN ISO 20567-1, method C). Here, a result of 0 after chipping is the best, with a result of 5 being the worst. A result of at most 1.5 is considered to be good. The results (average values of three panels) are likewise summarized in Table 2.

[0144] Table 2

[0145]

[0146]

[0147] In contrast, test panels made of aluminum alloy were subjected to a CASS test according to DIN EN ISO 9227 and a filiform test according to DIN EN 3665 for 240 hours. The results (average values of three panels) are summarized in Table 3.

[0148] Table 3

[0149]

[0150] iv) Results and discussion:

[0151] The scribe results of Table 1 clearly show the deterioration in coating adhesion in the case of nickel-free phosphatization as opposed to nickel-containing phosphatization on hot-dip galvanized and electrogalvanized steel (see VB2 vs. VB1 ; VB4 vs. VB3). By using the cleaning bath according to the application, in the case of the nickel-free variant, a coating adhesion can be achieved which almost corresponds to the nickel-containing variant (see B1 vs. VB1 and B2 vs. VB3).

[0152] Similar comments apply for the results of Table 2. Here the use of the inventive cleaning bath in nickel-free phosphating also achieves a significant improvement in corrosion protection values. This is further improved by the addition of gluconate and nitrite to the cleaning bath (see B1 versus B4).

[0153] The CASS and filiform results in Table 3 show that the use of the inventive cleaning bath in nickel-free phosphating on aluminium alloys achieves a significant improvement in corrosion protection values (see B3 versus VB5 and VB6). In the case of CASS as well as filiform, the corrosion protection achieved is in fact better than with the nickel-containing variant.

[0154] The comparison of Examples B6 and B7 (see Tables 1 and 2) shows that in each case the results achieved are further improved by the choice of a pH of 11.6 (B6) instead of a pH of 10.5 (B7).

[0155] The comparison of Examples B8 and B9 (see Tables 1 and 2) shows that in each case the results achieved are further improved by the choice of a pH of 11.3 (B8) instead of a pH of 10.5 (B9).

Claims

1. A process for the essentially nickel-free phosphating of metal surfaces, which comprises treating the metal surface successively with i) an alkaline aqueous cleaner composition comprising at least one water-soluble silicate, and then ii) an acidic aqueous and essentially nickel-free phosphating composition comprising zinc ions, manganese ions and phosphate ions.

2. The process according to claim 1, wherein the pH of the cleaner composition is from 10.7 to 12.0, preferably from 11.0 to 12.0, more preferably from 11.3 to 12.0, very preferably from 11.5 to 12.

0.

3. The process according to claim 1 or 2, wherein the metal surface is at least partially galvanized.

4. The process according to any of the preceding claims, wherein the at least one water-soluble silicate comprises at least one water glass and / or at least one metasilicate.

5. The process according to claim 4, wherein the at least one water-soluble silicate comprises at least one sodium water glass and / or potassium water glass.

6. The process according to any of the preceding claims, wherein the at least one water-soluble silicate is present in a total concentration of from 0.01 to 15, preferably from 0.2 to 13, more preferably from 0.5 to 10 g / l.

7. The process 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.

8. The process according to claim 7, wherein the at least one phosphorus-containing complexing agent comprises a pyrophosphate and / or a tripolyphosphate.

9. The process according to claim 7 or 8, wherein the at least one hydroxycarboxylic acid or salt thereof comprises a gluconate.

10. The process according to any of the preceding claims, wherein the cleaner composition comprises a nitrite.

11. The process according to any of the preceding claims, wherein the metal surface treated with the phosphating composition is further treated with an aqueous post-rinse composition comprising molybdenum ions and zirconium ions.

12. An alkaline aqueous cleaner composition comprising at least one water-soluble silicate according to any of the preceding claims.

13. A concentrate from which the cleaner composition according to claim 12 can be obtained by dilution with a suitable solvent and, if necessary, addition of a pH-adjusting substance.

14. A phosphate-coated metal surface obtainable by the process according to any of claims 1 to 11.

15. Use of the metal surface according to claim 14 in the automotive, automotive parts supplier or general industry sector. ​

Images