EP0922123B1 - Process and aqueous solution for phosphatising metallic surfaces - Google Patents

Description

The invention relates to an aqueous, phosphate-containing solution for the production of phosphate layers on metallic Surfaces made of iron, steel, zinc, zinc alloys, aluminum or aluminum alloys. The invention further relates to a Process for phosphating using an aqueous Phosphating solution.

DE-PS750957 discloses a method for improving the corrosion resistance of metals, in particular iron and steel, by treatment in a solution which forms phosphate coatings, in which the solution contains an accelerating agent and in which nitromethane, nitrobenzene, picric acid are used as accelerating agents , a nitraniline, a nitrophenol, a nitrobenzoic acid, a nitroresorcinol, nitrourea, a nitrourethane or nitroguanidine is used. The optimum concentration for the individual accelerators is different, but it is generally between 0.01 and 0.4% by weight in the phosphating solutions. The optimal concentration for the accelerator nitroguanidine should be 0.2% by weight. However, DE-PS750957 makes no information about the zinc content, the S value and the Zn-P ₂ O ₅ ratio of the phosphating solution.

DE-PS 977633 assumes that a phosphating bath cannot be operated solely with organic accelerators, since the iron accumulates more and more during the phosphating process in the bath, as a result of which the bath quickly becomes unusable and the phosphate layer becomes increasingly coarse-grained with increasing service life and thus gets worse in quality. Therefore, this document proposes a process for the production of phosphate coatings on ferrous metal objects in dilute, phosphoric acid solutions of the primary phosphates of zinc, manganese, cadmium, calcium and magnesium, in which the phosphating bath from time to time or continuously one or more organic accelerating agents, such as For example, nitroguanidine and hydrogen peroxide are added in such a way that the concentration of the organic accelerator in the bath is kept above 0.1% and at the same time a small excess of hydrogen peroxide is maintained in the bath over the amount required for the oxidation of the Fe ²⁺ ions. DE-PS 977633 therefore encourages the person skilled in the art to use nitroguanidine not only as an accelerator but always in combination with hydrogen peroxide.

DE-OS 38 00 835 discloses a process for phosphating metal surfaces, in particular surfaces made of iron, steel, zinc and their alloys and aluminum as a pretreatment for cold forming, in which the surface is activated without activation in the temperature range from 30 to 70 ° C in contact with an aqueous solution containing 10 to 40 g Ca ²⁺ / l, 20 to 40 g Zn ²⁺ / l, 10 to 100 g PO ₄ ^3- / l and as an accelerator 10 to 100 g NO ₃ ^- / l and / or 0.1 to 2.0 g of organic nitro compounds per liter, the solution having a pH in the range from 2.0 to 3.8 and a ratio of free acid to total acid of 1: 4 to 1: 100. An m-nitrobenzenesulfonate and / or nitroguanidine can be used as accelerator. The phosphate layers produced by the known method have layer weights of 3 to 9 g / m ² .

Although it is known per se that nitroguanidine in the Phosphating metallic surfaces as accelerators can be used, the practical use of this Accelerator on difficulties, because the achieved Results of the phosphating are very often unsatisfactory. This is obviously due to the effect of the accelerator nitroguanidine very strongly from the inorganic components of the phosphating solution and Concentration of inorganic components in the Phosphating solution is dependent, so that the under Use of nitroguanidine produced phosphate layers only then have good usage properties if one succeeds Provide phosphating solution in which the individual Components are coordinated so that at Use of nitroguanidine as an accelerator also in Continuous operation phosphate layers of good, consistent Quality can be generated. In addition, the Interactions between the nitroguanidine and the rest Components of the phosphating solution theoretical considerations or simple experiments are predicted or can be determined, but only by extensive Trial work on different phosphating systems are to be determined. The results are often unsatisfactory also on the poor water solubility or uneven distribution of nitroguanidine.

The invention is therefore based on the object of an aqueous Solution for phosphating metallic surfaces too create that contains nitroguanidine as an accelerator and the remaining components are coordinated so that the phosphate layers formed during the phosphating are fine crystalline, have a low layer weight, enable good paint adhesion and good Ensure protection against corrosion. Furthermore, the invention is the Task based on a process for phosphating create the phosphating solution according to the invention used, the method at the lowest possible Temperatures should work for phosphating different metallic surfaces can be used can and using simple technical means as well must work reliably.

The object on which the invention is based is achieved by the creation of an aqueous, phosphate-containing solution for producing phosphate layers on metallic surfaces made of iron, steel, zinc, zinc alloys, aluminum or aluminum alloy which contain 0.3 to 5 g of Zn ²⁺ / l, and Contains 0.1 to 3 g nitroguanidine / l, the S value being 0.03 to 0.3 and the weight ratio Zn: P ₂ O ₅ = 1: 5 to 1.30, and producing the fine-crystalline phosphate layers in which the crystallites have a maximum edge length of <15 µm. Surprisingly, it has been shown that the phosphating solution according to the invention can be used to produce very fine-crystalline phosphate layers which provide excellent paint adhesion and good corrosion protection. The crystallites have a plate-like, cuboid or cube-like shape and always have a maximum edge length of <15 µm, which is usually even <10 µm. Furthermore, the phosphating solution according to the invention is very suitable for phosphating cavities. The phosphate layers deposited on the metallic objects from the phosphating solution according to the invention have a layer weight of 1.5 to 4.5 g / m ² , preferably of 1.5 to 3 g / m ² , whereby the paint adhesion is favored in an advantageous manner. With a zinc content> 5 g / l, the corrosion protection properties and paint adhesion deteriorate significantly.

The Zn: P ₂ O ₅ ratio relates to the total P ₂ O _5. The determination of the total P ₂ O ₅ is based on the titration of the phosphoric acid and / or the primary phosphates from the equivalence point of the primary phosphate to the equivalence point of the secondary phosphate. The S value indicates the ratio of free acid, calculated as free P ₂ O ₅ , to total P ₂ O ₅ . The definitions and determination methods for total P ₂ O ₅ and free P ₂ O ₅ are explained in detail in the publication by W. Rausch "Die Phosphatierung von Metallen", 1988, pages 299 to 304.

According to the invention, it is particularly advantageous if the aqueous, phosphate-containing solution contains 0.3 to 3 g of Zn ²⁺ / l and 0.1 to 3 g of nitroguanidine / l, the S value being 0.03 to 0.3 and the weight ratio Zn: P ₂ O ₅ = 1: 5 to 1:30. With this solution according to the invention, which is suitable for carrying out the low zinc phosphating because of its zinc content of 0.3 to 3 g / l, particularly good work results have been achieved overall.

According to the invention it is provided that the aqueous solution contains 0.5 to 20 g NO ₃ ^- / l. The nitrate content according to the invention advantageously favors maintaining the optimal layer weight of 1.5 to 4.5 g / m ² . The nitrate is the phosphating solution in the form of alkali metal nitrates and / or by the cations present in the system, for. B. as zinc nitrate, and / or as HNO ₃ added. Since the nitrate-free aqueous solution also delivers good phosphating results, the known acceleration effect of the nitrate is in most cases of minor importance in the present case.

According to the invention it is further provided that the phosphating solution 0.01 to 3 g Mn ²⁺ / l and / or 0.01 to 3 g Ni ²⁺ / l and / or 1 to 100 mg Cu ²⁺ / l and / or Contains 10 to 300 mg Co ²⁺ / l. These metal ions are built into the phosphate layer and improve paint adhesion and corrosion protection.

In a further embodiment of the invention it is provided that the aqueous phosphating solution 0.01 to 3 g F ^- / l and / or 0.05 to 3.5 g / l complex fluoride, preferably (SiF ₆ ) ^2- or (BF ₄ ) ^- contains. The fluoride is added to the phosphating solution when metallic surfaces consisting of aluminum or aluminum alloys are to be phosphated. The complex fluorides are added to the phosphating solution, in particular for stabilization, whereby a longer service life of the phosphating baths is achieved.

The object underlying the invention is further achieved by the creation of a process for phosphating solved at who cleaned the metallic surfaces, then with the aqueous, phosphate-containing phosphating solution during a time of 5 seconds to 10 minutes at one temperature treated from 15 to 70 ° C and finally rinsed with water become. This procedure can be done with simple technical Funds are carried out and works extraordinarily reliable. The generated with the process Phosphate layers have a consistently good quality that even with a longer operating time of the phosphating bath does not decrease. The minimum phosphating time is at Process according to the invention less than in known Low zinc process with the usual accelerators work. The minimum phosphating time is the time in which the surface is 100% covered with a phosphate layer.

According to the invention it is provided that the treatment of the metallic surfaces with the phosphating solution is carried out by spraying, dipping, splash-dipping or rolling. These working techniques open up a very broad and diverse range of applications for the method according to the invention. According to the invention, it has proven to be particularly advantageous if the phosphating solution used for spraying has a weight ratio Zn: P ₂ O ₅ = 1:10 to 1:30 and if the phosphating solution used for dipping has a weight ratio Zn: P ₂ O ₅ = 1: 5 to 1:18.

After the invention, it is often advantageous if the metallic surfaces after cleaning with a Activating agents are treated, which is a titanium-containing Contains phosphate. This will form a closed, fine crystalline zinc phosphate layer supported.

Finally, it is provided according to the invention that the metallic surfaces after the one following the phosphating After-rinsing process treated with a passivating agent become. The passivating agents used can both Be Cr-containing as well as Cr-free.

In the case provided by the method according to the invention Cleaning the metallic surfaces will be both mechanical impurities as well as adhering fats from the surface to be phosphated removed. The cleaning of the metallic surfaces belongs to the known state of the art Technique and can be advantageous with an aqueous alkaline Cleaners are carried out. It is useful if the metallic surfaces rinsed with water after cleaning become. Rinsing the cleaned or the phosphated metallic surfaces are done either with tap water or with deionized water.

The phosphating solution according to the invention is thereby prepared that about 30 to 90 g of a concentrate, which the inorganic components of the phosphating solution and Contains water, be made up to 1 liter with water. Then the intended amount of nitroguanidine in Form a suspension or as a powder in the Phosphating solution introduced. The solution is then ready to use and during phosphating consumed substances can be added continuously by adding the Concentrate and the nitroguanidine are supplemented.

In order to avoid the difficult metering of the nitroguanidine as powder, the invention provides that the nitroguanidine is introduced into the aqueous solution in the form of a stabilized suspension. According to the invention, the suspension is stabilized with a layered silicate. This suspension contains 100 to 300 g nitroguanidine / l, 10 to 30 g layered silicate / l and the rest water. It can be easily pumped and is stable over 12 months, which means that the nitroguanidine does not settle even after a long time. The suspension is prepared by suspending the layered silicate in 1 liter of completely deionized water and then stirring in the nitroguanidine. At the pH of 2 to 3 in the phosphating solution, the suspension is destroyed and the nitroguanidine is released in a fine distribution. According to the invention have been used as layered silicates [Mg ₆ (Si _7.4 Al _0.6) O ₂₀ (OH) _4] Na _0.6 ^x xH ₂ O and [(Mg _5.4 Li _0.6) Si ₈ O ₂₀ (OH ₃ F) _4] Na _0.6 ^x xH ₂ O especially proven. These are synthetically produced three-layer silicates of the smectite type. The layered silicates have no adverse effect on the formation of the phosphate layers. In addition to their actual beneficial effect, they also improve the sedimentation of the phosphate sludge and increase its solids content.

The object of the invention is described below with reference to Exemplary embodiments explained in more detail.

a) Die Oberflächen von aus Stahlblech bestehenden metallischen Gegenständen wurden mit einem schwach alkalischen Reiniger (2%ige wässrige Lösung) während 5 Minuten bei 60 °C gereinigt und insbesondere entfettet.

b) Es folgte eine Spülung mit Leitungswasser während 0,5 Minuten bei Raumtemperatur.

c) Anschließend erfolgte eine Aktivierung mit einem Aktivierungsmittel (3 g/l H₂O), das ein Titanphosphat enthielt, während 0,5 Minuten bei Raumtemperatur.

d) Danach wurde bei ca. 55 °C während 3 Minuten durch Tauchen phosphatiert.

e) Schließlich wurde mit Leitungswasser während 0,5 Minuten bei Raumtemperatur gespült.

f) Die phosphatierten Oberflächen wurden mit Preßluft getrocknet.

Examples 1 and 2 were carried out using the following process steps:

a) The surfaces of sheet metal objects were cleaned with a weakly alkaline cleaner (2% aqueous solution) for 5 minutes at 60 ° C and degreased in particular.

b) This was followed by rinsing with tap water for 0.5 minutes at room temperature.

c) An activation with an activating agent (3 g / l H ₂ O), which contained a titanium phosphate, was then carried out for 0.5 minutes at room temperature.

d) It was then phosphated by dipping at about 55 ° C. for 3 minutes.

e) Finally, it was rinsed with tap water for 0.5 minutes at room temperature.

f) The phosphated surfaces were dried with compressed air.

The composition of those used for phosphating aqueous solutions and the properties of the phosphate layers are shown in Table 1.

In accordance with working examples 1 and 2, comparative tests were carried out with phosphating solutions known per se, but which contained a different accelerator (comparative tests A and B). In addition, a comparative test was carried out with a phosphating solution which was not in accordance with the Zn: P ₂ O ₅ ratio and which contained nitroguanidine as accelerator (comparative test C). In comparison tests A, B, C, process steps a) to f) were carried out. The composition of the phosphating solutions used for the comparative tests and the properties of the phosphate layers are shown in Table 2.

The comparison of the exemplary embodiments 1 and 2 with the comparative experiments A, B and C shows that good results are achieved with the phosphating solution according to the invention compared to the known and proven phosphating solutions, the nitroguanidine compared to the accelerator NO ₂ ^- but having much better utility properties. Comparative experiment C shows that good and practical phosphating results can only be achieved by using the parameters according to the invention.

Embodiments 3 and 4 were applied carried out the following process conditions, wherein in particular the suitability of the invention for phosphating Cavities should be checked: steel sheets were in one Box that simulated a cavity corresponding to the Process steps a) to e) treated, which also in the Embodiments 1 and 2 were used. The The phosphated steel sheets were dried in the cavity (Box) at room temperature without compressed air. The composition the aqueous used to phosphate a cavity Solutions and the properties of the phosphate layers result from Table 3.

The phosphate layers of working examples 3 and 4 had regarding layer weight, crystallite edge length and Minimum phosphating time about the same properties as that Phosphate layers of working examples 1 and 2.

According to the embodiments 3 and 4, the Comparative experiments D and E were carried out, the individual Process steps were identical. The two Comparative experiments D and E used phosphating solutions are known per se and contain accelerators Hydroxylamine. The composition of the to carry out the Comparative experiments D and E used solutions and the Properties of the phosphate layers are in Table 4 specified.

A comparison of the embodiments 3 and 4 with the Comparative experiments D and E show that with the invention very good phosphating of cavities can be achieved because according to the invention complete, creates closed phosphate layers, and a Flash rust does not occur. The term "rust formation" implies that on the metallic surface, the does not have a complete, closed phosphate layer, forms a rust layer during drying, which is very is disadvantageous. In some cases, rust formation remains from, although not a complete, closed phosphate layer what is present on a passivation of the metallic Surface due to the phosphating solution is likely to be based.

For testing the corrosion properties of and Paint adhesion on various, according to the invention were phosphated metallic substrates Paint adhesion test values determined.

Table 5 shows the paint adhesion and corrosion protection test values for different sheets (Substrates) were determined, the individual substrates according to Examples 5,6 and 7 with inventive Solutions and according to the comparative experiments F and G with known solutions have been phosphated by immersion. The The individual substrates were dipped in accordance with the Process steps a) to f) mentioned above. The Composition of the used for Examples 5, 6 and 7 Phosphating solutions are given in Table 7. There there are also the compositions of the known Phosphating solutions used to run the Comparative experiments F and G have been used. After An electrodeposition paint was used to phosphate the substrates by dipping, a filler and a top coat. Then the test was carried out by outdoor exposure, rated after 6 months, by a salt spray test and by falling rocks after a 12-round climate change test. Table 5 gives the results of the individual tests Infiltration of the lacquer layer, measured in mm, at, for the rockfall test called the paint flaking in percent is.

g) Die Oberflächen der Substrate wurden mit einem schwach alkalischen Reiniger (2 %-ige wässrige Lösung) während 5 Minuten bei 60°C gereinigt und insbesondere entfettet.

h) Es folgte eine Spülung mit Leitungswasser während 0,5 Minuten bei Raumtemperatur.

i) Danach wurde bei 55°C während 2 Minuten durch Spritzen phosphatiert.

k) Anschließend wurde mit einem chromfreien Nachspülmittel, das (ZrF₆)^2- enthielt, bei Raumtemperatur während 1 Minute gespült, um die phosphatierten Substrate zu passivieren.

l) Schließlich wurde mit vollentsalztem Wasser während 1 Minute bei Raumtemperatur gespült.

m) Die phosphatierten Substrate wurden im Ofen während 10 Minuten bei 80°C getrocknet.

Table 6 shows the paint adhesion and corrosion protection test values for various substrates that were phosphated by spraying. The spray phosphating of the substrates was carried out in accordance with the invention using the following process steps:

g) The surfaces of the substrates were cleaned with a weakly alkaline cleaner (2% aqueous solution) for 5 minutes at 60 ° C. and in particular degreased.

h) This was followed by a rinse with tap water for 0.5 minutes at room temperature.

i) It was then phosphated by spraying at 55 ° C. for 2 minutes.

k) It was then rinsed with a chromium-free rinse aid containing (ZrF ₆ ) ^2- at room temperature for 1 minute in order to passivate the phosphated substrates.

l) Finally, it was rinsed with deionized water for 1 minute at room temperature.

m) The phosphated substrates were dried in the oven at 80 ° C. for 10 minutes.

The composition of the aqueous Phosphating solutions required to carry out Examples 8, 9 and 10 were used are shown in Table 8. The Composition of the known phosphating solution for Execution of the comparative test H was used also in Table 8. On by spraying phosphated substrates was then a Electrocoat, a filler and a topcoat applied. The phosphated and painted substrates then became one Testing by outdoor exposure for 6 months a salt spray test, through a cross cut and through a 12-round climate change test with subsequent Subject to falling rocks. In Table 6 are those for test values determined for individual substrates, where for the cross cut a rating grade and for the Outdoor weathering, the salt spray test and the Climate change test measured the infiltration of the paint layer in mm. For the falling rocks the Paint flaking mentioned in percent.

The corrosion protection achieved by the phosphating according to the invention is comparable to the corrosion protection which occurs through the use of proven, known phosphating processes which work with the nitrite accelerator. The phosphating according to the invention, on the other hand, avoids the use of the accelerator nitrite, the use of which is increasingly being rejected, since nitrite produces reaction products during the phosphating which damage the environment and are sometimes toxic to humans. The paint adhesion and corrosion protection effect achieved by the phosphating according to the invention can be rated as very good to good. example 1 Example 2 Zn ²⁺ 1.4 g / l 1.4 g / l Mn ²⁺ 1.0 g / ll 1.0 g / l Ni ²⁺ 1.0 g / l - Cu ²⁺ - 8 mg / l NO ₃ ^- 3.0 g / l 3.0 g / l PO ₄ ^3- (total) 18.0 g / l 18.0 g / l = P ₂ O ₅ (total) 13.5 g / l 13.5 g / l Nitroguanidine 0.5 g / l 0.5 g / l Well ⁺ the amount required for titration data setting S value 0.09 0.09 Layer weight 2.4 g / m ² 2.6 g / m ² Crystallite edge length 2 - 8 µm 2 - 8 µm Minimum phosphating time <60 sec <60 sec Comparative experiment A Comparative experiment B Comparative experiment C Zn ²⁺ 1.4 g / l 1.4 g / l 3.5 g / l Ni ²⁺ 1.0 g / l 1.0 g / l - Mn ²⁺ 1.0 g / l 1.0 g / l - P ₂ O ₅ (total) 12.0 g / l 12.0 g / l 5.5 g / l S value 0.07 0.09 0.35 NO ₃ ^- 3.0 g / l 3.0 g / l 3.0 g / l H ₂ O ₂ 30 mg / l - - NO ₂ ^- - 170 mg / l - Nitroguanidine - - 2.0 g / l Well ⁺ the amount required for titration data setting Layer weight 1.3 g / m ² 2.2 g / m ² 4.9 g / m ² Crystallite edge length 40 µm 10 µm 20 to 25 µm Minimum phosphating time 120 sec 60 sec 60 sec Example 3 Example 4 Zn ²⁺ 1.4 g / l 1.9 g / l Ni ²⁺ 1.0 g / l 1.0 g / l Mn ²⁺ 1.0 g / l 1.0 g / l P ₂ O ₅ (total) 12.0 g / l 12.0 g / l S value 0.09 0.09 NO ₃ ^- 3.0 g / l 3.0 g / l Nitroguanidine 0.5 g / l 0.9 g / l Well ⁺ the amount required for titration data setting Complete, closed phosphate layer Yes Yes Film rust formation No No Comparative experiment D Comparative experiment E Zn ²⁺ 1.4 g / l 1.9 g / l Ni ²⁺ 1.0 g / l 1.0 g / l Mn ²⁺ 1.0 g / l 1.0 g / l P ₂ O ₅ (total) 12.0 g / l 12.0 g / l S value 0.09 0.09 NO ₃ ^- 3.0 g / l 3.0 g / l Hydroxylamine 1.0 g / l 1.0 g / l Well ⁺ the amount required for titration data setting Complete, closed phosphate layer No No Film rust formation Yes No Paint adhesion test values, immersion application Substrate Examples Comparative tests 5 6 7 F G Outdoor exposure 6 months, mm infiltration, measured on one side by the scratch. steel <1 <1 1.5 <1 2.5 Electrolytically galvanized steel 1 1 1 1.5 2.5 Hot-dip galvanized steel 0 <1 1 0 <1 Steel with Fe-Zn layer <1 <1 <1 <1 <1 AlMgSi, unpolished 3rd 0 0 <1 to 3 - AlMgSi, ground 5 <1 0 4th - Salt spray test, 1008 h, according to DIN 50021 SS, mm infiltration steel <1 <1 1.5 <1 1 12-round climate change test in accordance with VDA 621-415, infiltration in mm, measured on one side by the Ritz, and subsequent stone chipping in accordance with the specification of VW AG,% paint flaking, specified in () steel <1 (0.5) <1 (0.5) 1.5 (0.5) <1 (1) 2 (1) Electrolytically galvanized steel 6.5 (1.5) 7 (8.5) 7 (5) 5.5 (2) 8 (40) Hot-dip galvanized steel 1.5 (0.5) 2 (7) 2 (2) 1 (0.5) 2.5 (15) Steel with Fe-Zn layer 1 (0.5) 1 (0.5) 1 (0.5) 1 (0.5) 1 (0.5) Paint adhesion test values, spray application Substrate Examples Comparison test 8th 9 10th H Outdoor exposure 6 months, mm infiltration, measured on one side by the scratch. steel <1 1 <1 <1 Electrolytically galvanized steel <1 1.5 1.5 1.5 Hot-dip galvanized steel 0 0 0 0 Steel with Fe-Zn layer 0 <1 <1 <1 AlMgSi, unpolished 0 0 0 2nd AlMgSi, ground 0 0 2.5 5 Salt spray test, 1008 h, according to DIN 50021 SS, mm infiltration steel <1 <1 <1 <1 Cross cut after 240 h according to DIN 50017 KK and DIN / ISO 2409, grade steel 1 2 1 1 Electrolytically galvanized steel 1 1 1-2 1 Hot-dip galvanized steel 1 1 2nd 1 Steel with Fe-Zn layer 1 1 1 1 AlMgSi, unpolished 1 0 3rd 1 AlMgSi, ground 1 0-1 3rd 1 12-round climate change test in accordance with VDA 621-415, infiltration in mm, measured on one side by the Ritz, and subsequent stone chipping in accordance with the specification of VW AG,% paint flaking, specified in () steel <1 (2) 1 (5) <1 (2) <1 (2) Electrolytically galvanized steel 5 (5.5) 5.5 (9) 6 (14) 5.5 (4) Hot-dip galvanized steel 1.5 (1) 2.5 (2) 2.5 (1.5) 1.5 (1) Steel with Fe-Zn layer 1 (1) 1 (2) 1 (1) 1 (1) Substance / value Examples Comparative tests 5 6 7 F G Zn ²⁺ 1.4 g / l 1.4 g / l 1.4 g / l 1.4 g / l 3.5 g / l Mn ²⁺ 1.0 g / l 1.0 g / l 1.0 g / l 1.0 g / l - Ni ²⁺ 1.0 g / l - - 1.0 g / l - Cu ²⁺ - 8 mg / l - - - NO ₃ ^- 3.0 g / l 3.0 g / l 3.0 g / l 3.0 g / l 3.0 g / l P ₂ O ₅ (total) 13.5 g / l 13.5 g / l 13.5 g / l 12.0 g / l 5.5 g / l Nitroguanidine 0.5 g / l 0.5 g / l 0.5 g / l - 2 g / l NO ₂ ^- - - - 170 mg / l - S value 0.09 0.09 0.09 0.09 0.35 Substance / value Examples Comparison test 8th 9 10th H Zn ²⁺ 0.9 g / l 0.9 g / l 0.9 g / l 0.9 g / l Mn ²⁺ 1.0 g / l 1.0 g / l 1.0 g / l 1.0 g / l Ni ²⁺ 1.0 g / l - - 1.0 g / l Cu ²⁺ - 5 mg / l - - NO ₃ ^- 3.0 g / l 3.0 g / l 3.0 g / l 3.0 g / l P ₂ O ₅ (total) 11 g / l 11 g / l 11 g / l 11 g / l Nitroguanidine 0.5 g / l 0.5 g / l 0.5 g / l - NO ₂ ^- - - - 150 mg / l S value 0.07 0.07 0.07 0.07

Claims (17)

1. Aqueous, phosphate-containing solution for generating phosphate layers on metallic surfaces made of iron, steel, zinc, zinc alloys, aluminium or aluminium alloys, which solution contains zinc, phosphate as well as nitroguanidine as a catalyst, characterised in that the solution contains 0.3 to 5 g Zn²⁺/l and 0.1 to 3 g nitroguanidine/l, the S-value amounting to 0.03 to 0.3 and the weight ratio Zn to P₂O₅ = 1:5 to 1:30, the S-value indicating the ratio of free acid, calculated as free P₂O₅, to the total P₂O₅ and the solution generating fine-crystalline phosphate layers in which the crystallites have a maximum edge length < 15µm.
2. Aqueous solution according to claim 1, characterised in that the solution contains 0.3 to 3 g Zn²⁺/l.
3. Aqueous solution according to claims 1 to 2, characterised in that the solution contains 0.5 to 20 g NO₃ ^-/l.
4. Aqueous solution according to claims 1 to 3, characterised in that the solution contains 0.01 to 3 g Mn²⁺/l and/or 0.01 to 3 g Ni²⁺/l and/or 1 to 100 mg Cu²⁺/l and/or 10 to 300 mg Co²⁺/l.
5. Aqueous solution according to claims 1 to 4, characterised in that the solution contains 0.01 to 3 g F^-/l and/or 0.05 to 3.5 g/l of at least one complex fluoride.
6. Aqueous solution according to claims 1 to 5, characterised in that the solution contains (SiF₆)^2- or (BF₄)^- as the complex fluoride.
7. Method for phosphating, characterised in that the metallic surfaces are cleaned, subsequently treated with the aqueous, phosphate-containing solution in accordance with claims 1 to 6 during a time of between 5 seconds and 10 minutes at a temperature of 15 to 70°C and finally rinsed with water.
8. Method according to claim 7, characterised in that the treatment of the metallic surfaces with the phosphating solution takes place by spraying, immersing, spray immersing or roller application.
9. Method according to claim 8, characterised in that the phosphating solution used for spraying has a weight ratio Zn to P₂O₅ = 1:10 to 1:30.
10. Method according to claim 8, characterised in that the phosphating solution used for immersing has a weight ratio Zn to P₂O₅ = 1:5 to 1:18.
11. Method according to claims 7 to 10, characterised in that after the cleaning, the metallic surfaces are treated with an activating agent, which contains a titanium-containing phosphate.
12. Method according to claims 7 to 11, characterised in that after the rinsing process which follows the phosphating, the metallic surfaces are subsequently treated with a passivating agent.
13. Method according to claim 7, characterised in that the nitroguanidine is put into the aqueous solution in the form of a stable aqueous suspension.
14. Method according to claim 13, characterised in that the stable aqueous suspension contains a layer silicate as a stabiliser.
15. Method according to claim 14, characterised in that as a stabiliser, the layer silicates [Mg₆ (Si_7.4, Al_0.6) O₂₀ (OH)₄] Na_0.6 ·x XH₂O and [Mg_5.4 Li_0.6) Si₈ O₂₀ (OH₃ F)₄] Na_0.6 ·x XH₂O are used in an amount of 10 to 30 g/l of nitroguanidine solution.
16. Use of the aqueous phosphate-containing solution according to claims 1 to 6 and the method for phosphating according to claims 7 to 15 for treating work pieces before the lacquer coating.
17. Use according to claim 16 for treating work pieces before the electrophoretic painting.