EP0889977B1 - Zinc phosphatizing with low quantity of copper and manganese - Google Patents

Description

The invention relates to processes for phosphating metal surfaces with aqueous, acid phosphating solutions, the zinc and phosphate ions and a maximum of 70 ppm manganese and contain 30 ppm copper ions. The invention further relates to the use of such Process as pretreatment of the metal surfaces for a subsequent painting, in particular an electro dip coating or a powder coating. The procedure is applicable for the treatment of surfaces made of steel, galvanized or alloy galvanized Steel. Aluminum, aluminized or alloy-aluminized steel.

The phosphating of metals pursues the goal of being firmly adhered to the metal surface To produce metal phosphate layers that already improve the corrosion resistance and in connection with lacquers or other organic coatings to an essential Increased paint adhesion and resistance to infiltration when exposed to corrosion contribute. Such phosphating processes have long been known. For the Pretreatment before painting, especially electrocoating, is suitable especially the low-zinc phosphating processes, in which the phosphating solutions are comparatively high low levels of zinc ions of e.g. Have 0.5 to 2 g / l. An essential one The parameter in these low-zinc phosphating baths is the weight ratio of phosphate ions to zinc ions, which is usually in the range greater than 8 and assume values up to 30 can.

It has been shown that by using other polyvalent cations in the Zinc phosphating baths phosphate layers with significantly improved corrosion protection and Paint adhesion properties can be formed. For example, find low zinc processes with the addition of e.g. 0.5 to 1.5 g / l manganese ions and e.g. 0.3 to 2.0 g / l nickel ions as a so-called trication process for preparing metal surfaces for painting, for example for the cathodic electrocoating of car bodies, wide application.

Because nickel and the alternative cobalt can also be used from toxicological and wastewater engineering Classified as critical, there is a need for phosphating processes, which have a similar level of performance as the trication procedures, but with essential lower bath concentrations of nickel and / or cobalt and preferably without them get along with both metals.

A phosphating solution is known from DE-A-20 49 350, which as essential components 3 up to 20 g / l phosphate ions, 0.5 to 3 g / l zinc ions, 0.003 to 0.7 g / l cobalt ions or 0.003 to 0.04 g / l copper ions or preferably 0.05 to 3 g / l nickel ions, 1 to 8 g / l magnesium ions, 0.01 to 0.25 g / l nitrite ions and 0.1 to 3 g / l fluorine ions and / or 2 to 30 g / l chlorine ions contains. This method therefore describes a zinc-magnesium phosphating, where the phosphating solution additionally one of the ions cobalt, copper or preferably nickel contains. Such zinc-magnesium phosphating was not possible in technology push through.

EP-B-18 841 describes a chlorate-nitrite-accelerated zinc phosphating solution containing among others 0.4 to 1 g / l zinc ions. 5 to 40 g / l phosphate ions and optionally at least 0.2 g / l, preferably 0.2 to 2 g / l, of one or more ions selected from nickel, Cobalt, calcium and manganese. Accordingly, the optional manganese, nickel or Cobalt content at least 0.2 g / l. In the exemplary embodiments, nickel contents of 0.53 and 1.33 g / l stated.

EP-A-459 541 describes phosphating solutions which are essentially free of nickel and which contain 0.2 to 4 g / l manganese and 1 to 30 mg / l copper in addition to zinc and phosphate.

From DE-A-42 10 513 (= WO-A-93/20259) nickel-free phosphating solutions are known which contain 0.2 to 2 g / l zinc ions, 0.5 to 25 mg / l copper ions , 5 to 30 g / l phosphate ions (calculated as P ₂ O ₅ ) and hydroxylamine salts, hydroxylamine complexes and / or hydroxylamine in an amount of 500 to 5000 ppm hydroxylamine, based on the phosphating solution. Such phosphating solutions are used to treat metal surfaces selected from galvanized steel, galvanized alloy steel and aluminum and its alloys. The phosphating solutions can additionally contain 0.1 to 5 g / l, in particular 0.5 to 1.5 g / l, of manganese (II) ions. Other preferred components of this phosphating solution are alkaline earth metal cations, in particular magnesium and / or calcium ions, in an amount of up to 2.5 g / l. The phosphating solutions are essentially free of nitrate ions.

The phosphating processes described in the last two documents meet the requirements for corrosion protection. Thereby in In practice, however, phosphating baths are used which have a relatively high content Manganese of about 1 g / l. These phosphating baths therefore do not meet the requirements modern ecological requirements with the lowest possible levels Heavy metal ions to work, so that in the treatment of rinsing and Waste water produces as little metal-containing sludge as possible.

WO-A-94/08074 describes a method for phosphating galvanized steel surfaces by treating them with phosphating solutions which contain the following components: 0.1 to 5 g / l Zn ²⁺ cations, 5 to 50 g / l PO ₄ ³ anions, 0.1 to 50 g / l NO ₃ ^- anions and 0.1 to 5 g / l Mn ²⁺ cations and 0.001 to 1 g / l Cu ²⁺ cations. The following conditions are observed: pH value of the phosphating solutions in the range from 1.5 to 4.5, temperature of the phosphating solutions in the range from 10 to 80 ° C, treatment time in the range from 1 to 300 sec. During the phosphating process, the workpieces are treated cathodically with a direct current with a density in the range from 0.01 to 100 mA / cm ² .

EP-A-0 564 286 relates to a process for phosphating metal surfaces, selected from iron or zinc surfaces, with acid phosphating solutions, the 0.1 to 2.0 g / l zinc ions, 5 to 40 g / l phosphate ions, 0.001 to 3 g / l of a lanthanum compound (based on lanthanum metal), 0.1 to 3 g / l of manganese ions and contain a phosphating accelerator and a weight ratio of zinc ions to lanthanum metal in the range of 1: 0.01 to 1: 1.5. In addition these solutions can contain one or more of the following cations: 0.1 to 4 g / l cobalt ions, 0.01 to 3 g / l magnesium ions, 0.01 to 3 g / l calcium ions and 0.005 to 0.2 g / l copper ions.

0,2 bis 2 g/l Zinkionen

3 bis 50 g/l Phosphationen, berechnet als PO₄,

1 bis 70 mg/l Manganionen,

1 bis 30 mg/l Kupferionen und

einen oder mehrere Beschleuniger ausgewählt aus

0,3 bis 4 g/l Chlorationen,

0,01 bis 0,2 g/l Nitritionen,

0,05 bis 2 g/l m-Nitrobenzolsulfonationen,

0,05 bis 2 g/l m-Nitrobenzoationen,

0,05 bis 2 g/l p-Nitrophenol,

0,005 bis 0,15 g/l Wasserstoffperoxid in freier oder gebundener Form,

0,1 bis 10 g/l Hydroxylamin in freier oder gebundener Form,

0,1 bis 10 g/l eines reduzierenden Zuckers

enthält.The invention has for its object to provide a low-heavy phosphating process that achieves the performance of the trication phosphating process on the different materials used in automotive engineering. This object is achieved by a method for phosphating metal surfaces made of steel, galvanized or alloy galvanized steel and / or aluminum, in which the metal surfaces are sprayed or dipped for a time between 3 seconds and 8 minutes with a zinc-containing phosphating solution at a temperature between 30 and 70 ° C in contact, which has a weight ratio of phosphate ions to zinc ions between 3.7 and 30, characterized in that the phosphating solution is free of lanthanum compounds and that it

0.2 to 2 g / l zinc ions

3 to 50 g / l phosphate ions, calculated as PO ₄ ,

1 to 70 mg / l manganese ions,

1 to 30 mg / l copper ions and

one or more accelerators selected

0.3 to 4 g / l chlorate ions,

0.01 to 0.2 g / l nitrite ions,

0.05 to 2 g / l m-nitrobenzenesulfonate ions,

0.05 to 2 g / l m-nitrobenzoate ions,

0.05 to 2 g / l p-nitrophenol,

0.005 to 0.15 g / l hydrogen peroxide in free or bound form,

0.1 to 10 g / l hydroxylamine in free or bound form,

0.1 to 10 g / l of a reducing sugar

contains.

The zinc concentration is preferably in the range between about 0.3 and about 2 g / l and in particular between about 0.8 and about 1.6 g / l. Zinc levels above 1.6 g / l, for example between 2 and 3 g / l bring little advantages for the process, but can on the other hand increase the amount of sludge in the phosphating bath. Such zinc levels can change adjust a working phosphating bath when phosphating galvanized surfaces additional zinc gets into the phosphating bath due to the pickling removal. Nickel- and / or cobalt ions in the concentration range of about 1 to about 50 mg / l each for Nikkel and about 5 to about 100 mg / l for cobalt improve in conjunction with one if possible low nitrate content of no more than about 0.5 g / l against corrosion protection and paint adhesion Phosphating baths that do not contain nickel or cobalt or that contain nitrates of more than 0.5 g / l. This creates a favorable compromise between performance the phosphating baths on the one hand and the requirements for wastewater treatment the rinse water reached on the other hand.

From the German patent application with the file number 195 00 927.4 it is known that Lithium ions in the amount range from about 0.2 to about 1.5 g / l with zinc phosphating baths improve achievable corrosion protection. Lithium contents in the range from 0.2 to approximately 1.5 g / l and in particular from about 0.4 to about 1 g / l also have an effect on the invention low-heavy metal phosphating processes favorably on the achieved corrosion protection out.

If the process according to the invention is to be used as a spray process, copper contents are used particularly favorable in the range from about 0.002 to about 0.01 g / l. When using as Dipping processes copper contents in the range of 0.005 to 0.02 g / l are preferred.

Except for the cations mentioned above, which are incorporated into the phosphate layer or which at least have a positive effect on the crystal growth of the phosphate layer the phosphating baths usually sodium, potassium and / or ammonium ions for adjustment of free acid. The term free acid is known to the person skilled in the phosphating field common. The method of determination of free acid chosen in this document as well the total acidity is given in the example section. Free acid and total acid make you important control parameters for phosphating baths, since they have a great influence on the Have layer weight. Free acid values between 0 and 1.5 points for partial phosphating, with band phosphating up to 2.5 points and the total acidity between about 15 and about 30 points are within the technical range and are within the scope of this invention suitable.

It is common for phosphating baths that should be suitable for different substrates become free and / or complex bound fluoride in amounts up to 2.5 g / l total fluoride, add up to 1 g / l free fluoride. The presence of such amounts of fluoride is also advantageous for the phosphating baths according to the invention. In the absence of fluoride the aluminum content of the bath should not exceed 3 mg / l. In the presence of fluoride higher Al contents are tolerated as a result of the complex formation, provided the concentration of not complexed Al does not exceed 3 mg / l. The use of fluoride-containing baths is therefore advantageous if the surfaces to be phosphated are at least partially made of aluminum exist or contain aluminum. In these cases it’s cheap, not complex, but only free fluoride, preferably in concentrations in the range 0.5 to 1.0 g / l, to use.

For the phosphating of zinc surfaces, it would not be absolutely necessary that the Phosphating baths contain so-called accelerators. For the phosphating of Steel surfaces, however, require that the phosphating solution contain one or more Contains accelerator. Such accelerators are in the prior art as components of Zinc phosphating baths common. These are understood to mean substances that are caused by the When the acid is attacked by the acid on the metal surface, the resulting chemical chemical bind that they themselves are reduced. Accelerators with an oxidizing effect continue to have the effect of iron (II) ions released by the pickling attack on steel surfaces to the trivalent Oxidize stage so that they can precipitate as iron (III) phosphate.

0,3 bis 4 g/l Chlorationen,

0,01 bis 0,2 g/l Nitritionen,

0,05 bis 2 g/l m-Nitrobenzolsulfonationen,

0,05 bis 2 g/l m-Nitrobenzoationen,

0,05 bis 2 g/l p-Nitrophenol,

0,005 bis 0,15 g/l Wasserstoffperoxid in freier oder gebundener Form,

0,1 bis 10 g/l Hydroxylamin in freier oder gebundener Form,

0,1 bis 10 g/l eines reduzierenden Zuckers

The phosphating baths according to the invention can contain one or more of the following components as accelerators:

0.3 to 4 g / l chlorate ions,

0.01 to 0.2 g / l nitrite ions,

0.05 to 2 g / l m-nitrobenzenesulfonate ions,

0.05 to 2 g / l m-nitrobenzoate ions,

0.05 to 2 g / l p-nitrophenol,

0.005 to 0.15 g / l hydrogen peroxide in free or bound form,

0.1 to 10 g / l hydroxylamine in free or bound form,

0.1 to 10 g / l of a reducing sugar

When phosphating galvanized steel, it is necessary that the phosphating solution contains as little nitrate as possible. Nitrate concentrations of 0.5 g / l should not be exceeded because at higher nitrate concentrations there is a risk of so-called "speck formation" consists. This means white, crater-like defects in the phosphate layer. Moreover paint adhesion on galvanized surfaces is impaired.

The use of nitrite as an accelerator leads in particular to steel surfaces technically satisfactory results. For occupational safety reasons (risk of development nitrous gases) it is recommended to avoid nitrite as an accelerator. For phosphating galvanized surfaces, this is also advisable for technical reasons. since nitrite can form nitrate, which, as explained above, leads to the problem of Speck formation and reduced paint adhesion to zinc can result.

Hydrogen peroxide is for reasons of environmental friendliness, for technical reasons The simplified formulation options for replenishing solutions is hydroxylamine as Accelerators particularly preferred. Sharing these two accelerators is not advisable, however, since hydroxylamine is decomposed by hydrogen peroxide. You sit down Concentrations are hydrogen peroxide in free or bound form as an accelerator from 0.005 to 0.02 g / l of hydrogen peroxide are particularly preferred. The hydrogen peroxide be added to the phosphating solution as such. However, it is also possible Use hydrogen peroxide in bound form as compounds in the phosphating bath deliver hydrogen peroxide by hydrolysis reactions. Examples of such connections are persalts such as perborates, percarbonates, peroxosulfates or peroxodisulfates. As another Sources of hydrogen peroxide come from ionic peroxides such as alkali metal peroxides into consideration. A preferred embodiment of the invention is that a combination of chlorate ions and hydrogen peroxide in the phosphating process is used. In this embodiment, the concentration of chlorate for example in the range of 2 to 4 g / l, the concentration of hydrogen peroxide in the range 10 to 50 ppm.

The use of reducing sugars as accelerators is known from US-A-5 378 292. You can within the scope of the present invention in amounts between about 0.1 and about 10 g / l, preferably in amounts between about 0.5 and about 2.5 g / l. Examples Such sugars are galactose, mannose and especially glucose (dextrose).

Another preferred embodiment of the invention is as an accelerator To use hydroxylamine. Hydroxylamine can be used as a free base, as a hydroxylamine complex, as oxime, which is a condensation product of hydroxylamine with a ketone, or be used in the form of hydroxylammonium salts. Add free hydroxylamine the phosphating bath or a phosphating bath concentrate, it becomes due to the acid Character of these solutions largely exist as a hydroxylammonium cation. At a The sulfates and the phosphates are particularly suitable for use as the hydroxylammonium salt suitable. In the case of the phosphates, the acid salts are preferred due to the better solubility. Hydroxylamine or its compounds are used in the phosphating bath Amounts added that the calculated concentration of free hydroxylamine between 0.1 and 10 g / l, preferably between 0.3 and 5 g / l. It is preferred that the Phosphating baths as the only accelerator hydroxylamine, at most together with maximum 0.5 g / l nitrate. Accordingly, in a preferred embodiment, phosphating baths used that none of the other known accelerators such as Contain nitrite, oxo anions of halogens, peroxides or nitrobenzenesulfonate. As a positive As a side effect, hydroxylamine concentrations above about 1.5 g / l reduce the risk rust formation in insufficiently flooded areas of the components to be phosphated.

In practice it has been shown that the hydroxylamine accelerator is slow even then can be inactivated if there are no metal parts to be phosphated in the phosphating bath be introduced. It has surprisingly been found that the inactivation of the hydroxylamine can be significantly slowed down if you add the phosphating bath one or more aliphatic hydroxy or amino carboxylic acids with 2 to 6 carbon atoms in a total amount of 0.01 to 1.5 g / l. The carboxylic acids are preferred selected from glycine, lactic acid, gluconic acid, tartronic acid, malic acid, tartaric acid and citric acid, with citric acid, lactic acid and glycine being particularly preferred are.

When the phosphating process is applied to steel surfaces, iron goes in the form of Iron (II) ions in solution. If the phosphating baths according to the invention are not substances contain that have an oxidizing effect on iron (II), the divalent iron only goes into Result from air oxidation into the trivalent state, so that it is called ferric phosphate can fail. This is the case, for example, when using hydroxylamine. Therefore can build up iron (II) contents in the phosphating baths, which are clearly above the Laid down containing baths containing oxidizing agents. In this sense, iron (II) concentrations are up to 50 ppm normal, with short-term values in the production process up to 500 ppm can occur. Such are for the phosphating process according to the invention Iron (II) concentrations are not harmful. The phosphating baths can be used in hard water also the hardness cations Mg (II) and Ca (II) in a total concentration up to 7 mmol / l. Mg (II) or Ca (II) can also be used in the phosphating bath in quantities up to 2.5 g / l can be added.

The weight ratio of phosphate ions to zinc ions in the phosphating baths can vary within a wide range, provided that it is in the range between 3.7 and 30. A weight ratio between 10 and 20 is particularly preferred. For the indication of the phosphate concentration, the total phosphorus content of the phosphating bath is considered to be present in the form of phosphate ions PO ₄ ^3- . Accordingly, the known fact that the pH values of the phosphating baths, which are usually in the range from about 3 to about 3.6, only a very small part of the phosphate is actually in the form of the triple negative charged anions. At these pH values, it is rather to be expected that the phosphate is present primarily as a single negatively charged dihydrogenphosphate anion, together with smaller amounts of undissociated phosphoric acid and double negatively charged hydrogenphosphate anions.

Phosphating baths are usually sold in the form of aqueous concentrates which are adjusted to the application concentrations on site by adding water. For reasons of stability, these concentrates can contain an excess of free phosphoric acid, so that when diluted to a bath concentration, the value of the free acid is initially too high or the pH is too low. By adding alkalis such as sodium hydroxide, sodium carbonate or ammonia, the value of the free acid is reduced to the desired range. Furthermore, it is known that the free acid content during use of the phosphating baths can increase over time due to the consumption of the layer-forming cations and, if appropriate, through decomposition reactions of the accelerator. In these cases it is necessary to readjust the value of the free acid to the desired range from time to time by adding alkalis. This means that the contents of alkali metal or ammonium ions in the phosphating baths can fluctuate within wide limits and tend to increase over the course of the service life of the phosphating baths due to the dulling of the free acid. The weight ratio of alkali metal and / or ammonium ions to zinc ions, for example, can therefore be very low in freshly prepared phosphating baths, for example <0.5 and in extreme cases even 0, while it usually increases over time due to bath maintenance measures, so that the ratio> 1 and can take values up to 10 and larger. Low-zinc phosphating baths generally require additions of alkali metal or ammonium ions in order to be able to adjust the free acid to the desired value range at the desired weight ratio PO ₄ ^3- : Zn> 8. Analogous considerations can also be made regarding the proportions of alkali metal and / or ammonium ions to other bath components, for example phosphate ions.

In the case of lithium-containing phosphating baths, the use of is preferably avoided Sodium compounds to adjust the free acid, because of too high sodium concentrations the beneficial effect of lithium on corrosion protection is suppressed. In this If possible, basic lithium compounds are preferably used to adjust the free acid. In the alternative, potassium compounds are also suitable.

In principle, it does not matter in what form the layer-forming or layer-influencing Cations are introduced into the phosphating baths. However, nitrates should be avoided in order not to exceed the preferred upper limit of the nitrate content. Preferably sets one enters the metal ions in the form of such compounds that no foreign ions in the phosphating solution enter. Therefore, it is most convenient to use the metals in the form of their oxides or their carbonates. Lithium can also be used as sulfate, copper preferably as acetate be used.

Phosphating baths according to the invention are suitable for phosphating surfaces Steel, galvanized or alloy galvanized steel, aluminum, aluminized or alloy aluminized Steel. The term "aluminum" includes the technically usual aluminum alloys such as AlMg0.5Si1.4. The materials mentioned can - as is becoming increasingly common in automotive engineering - also exist side by side.

Parts of the bodywork can also consist of material that has already been pretreated, such as is produced using the Bonazink ^R process. The base material is first chromated or phosphated and then coated with an organic resin. The phosphating process according to the invention then leads to phosphating on damaged areas of this pretreatment layer or on untreated rear sides.

The process is suitable for use in immersion, spray or spray / immersion processes. It can be used in particular in automobile construction, where treatment times between 1 and 8 minutes, especially 2 to 5 minutes, are usual. Use in tape phosphating in the steel mill, with treatment times between 3 and 12 seconds however also possible. It is recommended when used in tape phosphating processes. the bath concentrations in each case in the upper half of the preferred according to the invention Areas. For example, the zinc content can range from 1.5 to 2.0 g / l and the free acid content is in the range of 1.5 to 2.5 points. As a substrate for strip phosphating is particularly suitable for galvanized steel, especially electrolytically galvanized steel.

As is also common with other phosphating baths of the prior art, the most suitable ones are Bath temperatures regardless of the area of application between 30 and 70 ° C, whereby the temperature range between 45 and 60 ° C is preferred.

The phosphating process according to the invention is in particular for the treatment of the named Metal surfaces before painting, for example before cathodic electro-painting thought as it is common in automotive engineering. It is also suitable as a pretreatment before a powder coating, such as that used for household appliances becomes. The phosphating process is part of the technically usual pretreatment chain to see. In this chain, the steps of cleaning / degreasing are usually the Intermediate rinsing and activation upstream, the activation usually with activating agents containing titanium phosphate. The phosphating according to the invention can, with or without intermediate rinsing, optionally a passivating aftertreatment consequences. Chromic acid-containing ones are used for such a passivating aftertreatment Treatment baths widely used. For reasons of work and environmental protection as well as from For disposal reasons, however, there is a tendency to pass these chromium-containing passivation baths through to replace chrome-free treatment baths. Purely inorganic bath solutions are particularly useful for this based on zirconium compounds, or also organic reactive bath solutions, for example based on poly (vinylphenols). From the German patent application with the file number 195 11 573.2 it is known that certain phosphating processes passivating rinsing with an aqueous solution with a pH in the range of to follow about 3 to about 7, the 0.001 to 10 g / l of one or more of the following Cations contain: lithium ions, copper ions and / or silver ions. Such a rinse is also suitable for improving the corrosion protection of the phosphating process according to the invention. An aqueous solution which is 0.002 to 1 g / l contains copper ions. The copper is preferably used as acetate. Especially such a rinsing solution is preferred which has a pH in the range from 3.4 to 6 and has a temperature in the range of 20 to 50 ° C.

Between this post passivation and the usually subsequent painting an intermediate rinse with deionized water is usually carried out.

Embodiments

1. Reinigen mit einem alkalischen Reiniger (Ridoline^R 1501, Henkel KGaA), Ansatz 2 % in Stadtwasser, 55 °C, 4 Minuten.

2. Spülen mit Stadtwasser, Raumtemperatur, 1 Minute.

3. Aktivieren mit einem Titanphosphat-haltigen Aktiviermittel (Fixodine^R 950, Henkel KGaA), Ansatz 0,1 % in vollentsalztem Wasser, Raumtemperatur, 1 Minute.

4. Phosphatieren mit Phosphatierbädern gemäß Tabelle 1, 4 Minuten, Temperatur 55 °C. Außer den in Tabelle 1 genannten Kationen enthielten die nitratfreien Phosphatierbäder 0,1 g/l Eisen (II) und erforderlichenfalls Natriumionen zum Einstellen der freien Säure. Li-haltige Phosphatierbäder enthielten kein Natrium. Alle Bäder enthielten 0,95 g/l SiF₆- und 0,2 g/l F^- sowie als Beschleuniger 1,7 g/l Hydroxylammoniumsulfat. Die Punktzahl der freien Säure betrug 1,0 - 1,1, der Gesamtsäure 23-25. Unter Punktzahl der freien Säure wird der Verbrauch in ml an 0,1-normaler Natronlauge verstanden, um 10 ml Badlösung bis zu einem pH-Wert von 3,6 zu titrieren. Analog gibt die Punktzahl der Gesamtsäure den Verbrauch in ml bis zu einem pH-Wert von 8,2 an.

5. Spülen mit Stadtwasser, Raumtemperatur, 1 Minute.

6. Nachpassivieren mit einem chromfreien Nachpassivierungsmittel auf Basis komplexer Zirkonfluoride (Deoxylyte^R 54 NC, Henkel KGaA) 0,25 %-ig in vollentsalztem Wasser, pH 4.0. Temperatur 40 °C, 1 Minute.

7. Spülen mit vollentsalztem Wasser.

8. Trockenblasen mit Preßluft

The phosphating processes and comparative processes according to the invention were checked on steel sheets ST 1405 and on electrolytically galvanized steel sheets, as are used in automobile construction. The following process, common in body production, was carried out as an immersion process:

1.Clean with an alkaline cleaner (Ridoline ^R 1501, Henkel KGaA), mix 2% in city water, 55 ° C, 4 minutes.

2. Rinse with city water, room temperature, 1 minute.

3. Activation with an activating agent containing titanium phosphate (Fixodine ^R 950, Henkel KGaA), approach 0.1% in deionized water, room temperature, 1 minute.

4. Phosphating with phosphating baths according to Table 1, 4 minutes, temperature 55 ° C. In addition to the cations listed in Table 1, the nitrate-free phosphating baths contained 0.1 g / l of iron (II) and, if necessary, sodium ions to adjust the free acid. Li-containing phosphating baths did not contain sodium. All baths contained 0.95 g / l SiF ₆ - and 0.2 g / l F ^- and 1.7 g / l hydroxylammonium sulfate as accelerator. The free acid score was 1.0-1.1, the total acid 23-25. The free acid score is understood to mean the consumption in ml of 0.1 normal sodium hydroxide solution in order to titrate 10 ml of bath solution up to a pH of 3.6. Similarly, the total acid score indicates consumption in ml up to a pH of 8.2.

5. Rinse with city water, room temperature, 1 minute.

6. Post-passivation with a chrome-free post-passivation agent based on complex zirconium fluoride (Deoxylyte ^R 54 NC, Henkel KGaA) 0.25% in deionized water, pH 4.0. Temperature 40 ° C, 1 minute.

7. Rinse with deionized water.

8. Blow dry with compressed air

The mass per unit area ("layer weight") was determined by dissolving in 5% chromic acid solution in accordance with DIN 50942. It was in the range 2.5-4.5 g / m ²

The phosphated test panels were coated with a cathodic dip coating from BASF (FT 85-7042) coated. The corrosion protection effect for electrolytically galvanized steel was tested in an alternating climate test according to VDA 621-415 over 5 laps. As a result the paint infiltration at the Ritz (half the width of the Ritz) is shown in Table 1. Table 1 also contains as "K-values" the results of a stone chip test according to the VW standard (the smaller K, the better the paint adhesion).

The corrosion protection for steel sheets was tested with a salt spray test according to DIN 50021 (1008 hours). Table 1 contains the paint infiltration at the Ritz (half of the Ritz width).

Claims (9)

1. A process for phosphating metal surfaces of steel, galvanized or alloy-galvanized steel and/or of aluminium in which the metal surfaces are contacted by spraying or dipping for 3 seconds to 8 minutes with a zinc-containing phosphating solution having a temperature of 30 to 70°C, characterized in that the phosphating solution contains 0.2 to 2 g/l zinc ions, 3 to 50 g/l phosphate ions expressed as PO₄, 1 to 70 mg/l manganese ions, 1 to 30 mg/l copper ions and one or more accelerators selected from 0.3 to 4 g/l chlorate ions, 0.01 to 0.2 g/l nitrite ions, 0.05 to 2 g/l m-nitrobenzenesulfonate ions, 0.05 to 2 g/l m-nitrobenzoate ions, 0.05 to 2 g/l p-nitrophenol, 0.005 to 0.15 g/l hydrogen peroxide in free or bound form, 0.1 to 10 g/l hydroxylamine in free or bound form and 0.1 to 10 g/l of a reducing sugar.
2. A process as claimed in claim 1, characterized in that the phosphating solution additionally contains 1 to 50 mg/l nickel ions and/or 5 to 100 mg/l cobalt ions.
3. A process as claimed in one or both of claims 1 and 2, characterized in that the phosphating solution additionally contains 0.2 to 1.5 g/l lithium ions.
4. A process as claimed in one or more claims 1 to 3, characterized in that the phosphating solution contains 5 to 20 mg/l copper ions where it is applied by dipping and 2 to 10 mg/l copper ions where it is applied by spraying.
5. A process as claimed in one or more of claims 1 to 4, characterized in that the phosphating solution additionally contains fluoride in quantities of up to 2.5 g/l total fluoride, of which up to 1 g/l is free fluoride, expressed as F^-.
6. A process as claimed in one or more of claims 1 to 5, characterized in that the phosphating solution contains 5 to 150 mg/l hydrogen peroxide in free or bound form as accelerator.
7. A process as claimed in one or more of claims 1 to 5, characterized in that the phosphating solution contains 0.1 to 10 g/l hydroxylamine in free or bound form as accelerator.
8. A process as claimed in claim 7, characterized in that the phosphating solution additionally contains a total of 0.01 to 1.5 g/l of one or more aliphatic hydroxycarboxylic or aminocarboxylic acids containing 2 to 6 carbon atoms.
9. A process as claimed in one or more of claims 1 to 8, characterized in that, after their treatment with the phosphating solution and before painting, the metal surfaces are subjected to a passivating post-rinse with an aqueous solution with a pH of 3 to 7 containing a total of 0.001 to 10 g/l of one or more of the following cations: lithium ions, copper ions and/or silver ions.