EP0760870B1 - Iron phosphatisation using substituted monocarboxilic acids - Google Patents

Abstract

PCT No. PCT/EP95/01815 Sec. 371 Date Sep. 9, 1997 Sec. 102(e) Date Sep. 9, 1997 PCT Filed May 12, 1995 PCT Pub. No. WO95/32319 PCT Pub. Date Nov. 30, 1995Described are a concentrate, a working solution and a process for iron phosphating of metals, in which the solution contains nitrobenzene sulfonic acid and substituted short-chain monocarboxylic acids of the amino acid and/or hydroxycarboxylic acid type as the accelerators.

Description

The invention relates to a new phosphating solution for the so-called non-layer-forming phosphating of reactive metal surfaces, in particular Surfaces made of steel, aluminum, zinc or alloys whose Main component of at least one of the metals iron, aluminum or zinc represents. With non-layer-forming phosphating, the metal surfaces with acidic solutions (pH range between 3.5 and 6) from Treated phosphates, which creates a layer on the metal surface from phosphates and / or oxides, their cations from the metal surface and do not come from other components of the phosphating bath. This distinguishes the "non-layer-forming" Iron phosphating from a "layer-forming" zinc phosphating, at the cations of the phosphating bath are built into the phosphate layer. Processes for iron phosphating are known in the prior art. she are used, for example, as a pretreatment process before painting used in cases where there is no excessive corrosive load of the components is to be expected.

In order to meet the corrosion protection requirements, it is desirable that the iron phosphate layers have a mass per unit area (layer weight) of above about 0.2 g / m ² . In principle, the corrosion protection effect increases with increasing layer weight. With higher layer weights, for example above about 0.8 g / m ² , there is a risk that the layers become powdery and do not adhere firmly to the metal surface. This leads to an unacceptably poor paint adhesion. Efforts are therefore being made to produce iron phosphate layers which, on the one hand, achieve the highest possible layer weight, for example in the range between approximately 0.5 and approximately 1 g / m ² , the coverings at the same time being intended to form firmly adhering layers.
It is known that the layer formation is very strongly influenced by the presence of so-called "accelerators". Such accelerators are inorganic or organic substances with an oxidizing, more rarely with a reducing effect. Inorganic accelerators are, for example, nitrates, chlorates, bromates, molybdates and tungstates. Known organic accelerators are aromatic nitro compounds such as nitrobenzenesulfonic acid, especially m-nitrobenzenesulfonic acid ("NBS"). An example of an inorganic substance with a rather reducing effect and with good accelerator properties is hydroxylamine and its salts. Phosphating baths containing such accelerator systems are known, for example, from US Pat. No. 5,137,589 and WO93 / 09266. According to the last-mentioned document, particularly good layers are produced when oxidizing and reductive accelerators are combined with one another, here, for example, hydroxylamine with organic nitro compounds, with molybdate or tungstates.

When using a molybdate accelerator, relatively thin layers (0.2 to 0.5 g / m ² ) are obtained, which usually have a bluish tinge. With organic accelerators, thicker layers of up to 1 g / m ² can be achieved, which generally offer significantly better corrosion protection against rust penetration. With phosphate layer weights over 0.5 g / m ² one speaks of a thick layer iron phosphating, with layer weights under 0.5 g / m ² a thin layer iron phosphating.

Furthermore, it is known that the formation of iron phosphate layers is favorably influenced if the phosphating solution chelating complexing agents for iron contains. According to US Pat. No. 5,137,589, gluconic acid is used for this particularly suitable. The CA-874944 continues to recommend the use of ethylenediaminetetraacetic acid, nitrilotriacetic acid, Diethylenetriaminepentaacetic acid, citric acid, tartaric acid and Glucoheptonic acid. The complexing agents mentioned have in common that they chelating carboxylic acids with at least 4 carbon atoms and with at least 3 represent substituents selected from carboxyl and hydroxyl groups.

Modern iron phosphating baths are expected to do more than just that Iron surfaces, but also surfaces made of zinc, aluminum and their Alloys can be treated. Thereby on aluminum and zinc although no or at most very thin phosphate layers formed by the If the acid is attacked, the paint adhesion is somewhat improved. Disadvantageous the influence of this so-called mixed driving style of the aluminum ions going into solution, which start at a very low level Concentration leads to the disruption of the formation of the iron phosphate layer. This can be done by adding fluorides to the phosphating baths Complex "bad poison" and thus render it harmless. A fluoride additive at the same time improves the pickling effect on aluminum surfaces. Here it has proven to be beneficial if the treatment solutions are free and / or contain complex-bound fluoride (W093 / 09266).

EP-A-398 203 shows that iron phosphating solutions instead the usual accelerator anionic titanium compounds, preferably in a concentration between 0.05 and 0.2 g / l dissolved titanium can.

When iron phosphating can be done so that the metal parts first cleaned in a detergent solution and then the cleaned Parts treated in a phosphating bath. In this case Phosphating bath itself have no cleaning effect. This procedure provides better cleaning and phosphating results, but requires a higher number of treatment baths. Alternatively, it is possible to clean dirty metal parts in a bath at the same time and to phosphate. In this case it is necessary to use the phosphating bath Add surfactants, preferably nonionic. According to W093 / 09266 for this purpose, for example, ethoxylated alcohols with 12 to 22 carbon atoms, others modified aromatic or aliphatic polyethers and salts complex organic phosphoric acid esters.

Finally, GB-A-741.050 describes a non-layer-forming phosphating process for Metal surfaces described, in which the acid phosphating baths 0.1 to 3 wt .-% Contain tartaric acid or its salts. This additive makes the formation more powdery Prevents phosphate coatings. The phosphating baths have a pH in the range from 4.2 to 5.8 and are based on phosphate solutions of non-layer-forming metals and Oxidizing agents. It is mentioned that an addition of other compounds, such as Citric acid, lactic acid, glycolic acid, aminoacetic acid and its salts, the formation such powdery coatings not prevented.

The invention has for its object an iron phosphating solution with an ecological to provide cheap accelerator system. It was found. that ecologically safe substituted monocarboxylic acids combined lead with the co-accelerator nitrobenzenesulfonic acid to phosphate layers that the meet technical requirements.

a) 1 bis 20 g/l gelöstes Phosphat,

b) 0,02 bis 2 g/l Nitrobenzolsulfonsäure,

c) Wasser und erwünschtenfalls weitere Hilfsstoffe,

dadurch gekennzeichnet, daß die Lösung außerdem

d) 0,01 bis 0,8 g/l einer oder mehrerer organischer Monocarbonsäuren der allgemeinen Formel (I)

enthält, wobei

R = H, CH₃, CH₂Y, C₂H₅, C₂H₄Y, C₆H₅, C₆H₄Y oder C₆H₃Y₂,

X und Y unabhängig voneinander NH₂ oder OH und

n = 0, 1 oder 2

bedeuten.The invention accordingly relates to an aqueous solution for iron phosphating metals containing a pH in the range from 3.5 to 6

a) 1 to 20 g / l dissolved phosphate,

b) 0.02 to 2 g / l nitrobenzenesulfonic acid,

c) water and, if desired, other auxiliaries,

characterized in that the solution also

d) 0.01 to 0.8 g / l of one or more organic monocarboxylic acids of the general formula (I)

contains, where

R = H, CH ₃ , CH ₂ Y, C ₂ H ₅ , C ₂ H ₄ Y, C ₆ H ₅ , C ₆ H ₄ Y or C ₆ H ₃ Y ₂ ,

X and Y independently of one another NH ₂ or OH and

n = 0, 1 or 2

mean.

Depending on the choice of the substituent X, the above formula (I) describes either amino acids (X = NH ₂ ) or hydroxycarboxylic acids (X = OH). When choosing amino acids, α-amino acids are preferred. They are described by the general formula (1) in that the index n = 0. The amino acids are preferably selected from glycine, alanine, serine, phenylalanine, (hydroxyphenyl) alanine and (dihydroxyphenyl) alanine, with glycine, alanine and serine being particularly preferred.

The hydroxycarboxylic acids of general characterized by X = OH Formula (I) are preferably selected from glycolic acid and lactic acid.

Phosphating solutions containing 0.1 to 0.8 g / l, preferably 0.2 to 0.4 g / l of one or more carboxylic acids of the general Contain formula (I).

Particularly favorable phosphating results are achieved with phosphating solutions achieved that contain 0.2 to 0.5 g / l nitrobenzenesulfonic acid. Doing so preferably the m-nitrobenzenesulfonic acid ("NBS") is used.

The substituted carboxylic acids described by the general formula (I) are usually optically active. For the use according to the invention it is irrelevant whether the acids are in the form of a racemate or in the R or L form available.

The acids mentioned, including phosphoric acid, can be used as such or can be used as alkali or ammonium salts. The pH must be correct the phosphating solution to the effective range between about 3.5 and about 6.0 can be set. If necessary, this can be done by adding Acid, preferably phosphoric acid, or of lye, preferably sodium hydroxide solution, respectively. These are under these pH conditions Acids according to their respective pK values partly in undissociated Form before.

e) 0,05 bis 3 g/l freies und/oder komplexgebundenes Fluorid. Dabei ist es gemäß der W093/09266 empfehlenswert, daß die Lösung sowohl freies als auch komplexgebundenes Fluorid enthält. Als Quelle für freies Fluorid kommen beispielsweise Flußsäure sowie Alkalimetall- und/oder Ammoniumfluoride in Betracht, als Quelle für komplexgebundenes Fluorid beispielsweise Tetrafluoroborate, Hexafluorotitanate, Hexafluorozirkonate, Hexafluorosilicate oder jeweils deren Säuren.

f) 0,1 bis 6 g/l einer chelatisierenden Carbonsäure mit mindestens 4 C-Atomen und mindestens 3 Substituenten ausgewählt aus Carboxyl- und Hydroxy-Gruppen. Beispiele solcher chelatisierender Carbonsäuren sind Zuckersäuren wie Gluconsäure, mehrbasische Hydroxycarbonsäuren wie Weinsäure und Citronensäure sowie von tertiären Aminen abgeleitete Carbonsäuren wie Ethylendiamintetraessigsäure, Diethylentriaminpentaessigsäure oder Nitrilotriessigsäure. Gluconsäure ist besonders bevorzugt.

g) 0,02 bis 20 mMol/l Molybdat und/oder Wolframat. Dabei kann es sich im einfachsten Falle um Salze der Molybdänsäure H₂MoO₄ und/oder der Wolframsäure H₂WO₄ handeln. Die wolfram- oder molybdänhaltigen Anionen könne aber auch in kondensierter Form vorliegen und für Molybdän beispielsweise durch die allgemeine Formel [Mo_nO_(3n+1)]^2- beschrieben werden.

h) 0,02 bis 1 g/l einer anionischen Titanverbindung gemäß der Lehre der EP-A-398 203, und/oder eine entsprechende Menge einer anionischen Zirkonverbindung, jeweils bezogen auf die Menge der Anionen. Hierfür sind insbesondere Hexafluorotitansäure, Hexafluorozirkonsäure oder deren Alkalimetall- oder Ammoniumionen geeignet. Vorzugsweise wählt man die Konzentrationen der Anionen im Bereich 0,05 bis 0,5 g/l.

i) bis zu 40 g/l, vorzugsweise 0,2 bis 1 g/l und insbesondere 0,3 bis 0,5 g/l Tenside, vorzugsweise nichtionische Tenside vom Typ der Fettalkoholethoxylate. Solche Tenside sind insbesondere dann erforderlich, wenn die Phosphatierlösung gleichzeitig reinigend wirken soll. Je nach Schaumneigung der Tenside, die vorzugsweise möglichst gering sein soll, kann es erforderlich sein, zusammen mit den Tensiden entschäumend wirkende Substanzen wie beispielsweise Blockcopolymere aus Ethylenoxid und Propylenoxid zu verwenden. Weiterhin kann es, insbesondere bei höheren Tensidgehalten, erforderlich sein, zur Formulierung homogener Konzentrate der Behandlungslösungen sogenannte Hydrotrope einzusetzen. Hierfür sind beispielsweise Toluol-, Xylol- oder Cumolsulfonate geeignet, deren hydrotrope Wirkung durch Zugabe wasserlöslicher komplexer organischer Phosphorsäureester unterstützt werden kann.

k) 0,05 bis 5 g/l Nitrat.

The phosphating solution according to the invention can contain further auxiliaries known in the prior art. Examples include:

e) 0.05 to 3 g / l free and / or complex-bound fluoride. According to W093 / 09266, it is recommended that the solution contain both free and complex-bound fluoride. Examples of possible sources of free fluoride are hydrofluoric acid and alkali metal and / or ammonium fluorides, and sources of complex-bound fluoride are, for example, tetrafluoroborates, hexafluorotitanates, hexafluorozirconates, hexafluorosilicates or their respective acids.

f) 0.1 to 6 g / l of a chelating carboxylic acid with at least 4 carbon atoms and at least 3 substituents selected from carboxyl and hydroxyl groups. Examples of such chelating carboxylic acids are sugar acids such as gluconic acid, polybasic hydroxycarboxylic acids such as tartaric acid and citric acid, and carboxylic acids derived from tertiary amines such as ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid or nitrilotriacetic acid. Gluconic acid is particularly preferred.

g) 0.02 to 20 mmol / l molybdate and / or tungstate. In the simplest case, these can be salts of molybdic acid H ₂ MoO ₄ and / or tungsten acid H ₂ WO ₄ . However, the anions containing tungsten or molybdenum can also be present in condensed form and described for molybdenum, for example, by the general formula [Mon _n O _{(3n + 1)} ] ^2- .

h) 0.02 to 1 g / l of an anionic titanium compound according to the teaching of EP-A-398 203, and / or a corresponding amount of an anionic zirconium compound, in each case based on the amount of the anions. Hexafluorotitanic acid, hexafluorozirconic acid or their alkali metal or ammonium ions are particularly suitable for this. The concentrations of the anions are preferably selected in the range from 0.05 to 0.5 g / l.

i) up to 40 g / l, preferably 0.2 to 1 g / l and in particular 0.3 to 0.5 g / l surfactants, preferably nonionic surfactants of the fatty alcohol ethoxylate type. Such surfactants are particularly necessary if the phosphating solution is to have a cleaning effect at the same time. Depending on the tendency of the surfactants to foam, which should preferably be as low as possible, it may be necessary to use defoaming substances together with the surfactants, such as block copolymers of ethylene oxide and propylene oxide. Furthermore, it may be necessary, especially with higher surfactant contents, to use so-called hydrotropes to formulate homogeneous concentrates of the treatment solutions. For this purpose, for example, toluene, xylene or cumene sulfonates are suitable, the hydrotropic effect of which can be supported by adding water-soluble complex organic phosphoric acid esters.

k) 0.05 to 5 g / l nitrate.

When incorporated, the iron phosphating baths usually have Iron (II) levels up to about 25 ppm, which has positive bathing properties influence. When it comes to new phosphating solutions, it is recommendable to add iron (II) ions in the ppm range, for example by adding about 20-50 ppm iron (II) sulfate.

Phosphating solutions continue to be characterized by their "total acid" content, expressed in points, characterized. Here one understands the Total acid score the consumption in milliliters of 0.1 N sodium hydroxide solution, 10 ml of the solution up to the point of transition of phenolphthalein or titrate up to a pH of 8.5. Technically common areas of Total acid are between about 3 and about 7 points, preferably between about 4 and about 6 points.

The temperatures of the treatment solutions are usually between about 30 and 70 ° C. The bath temperature is particularly suitable for cleaning acting baths according to the type and amount of pollution as well as the intended Treatment time. The minimum temperature depends on the foam behavior of the wetting agents used and is preferably above the Cloud point of the wetting agent selected. Usually the temperature is between 50 and 60 ° C. The workpieces to be treated can with the Solution splashed or immersed in the solution. Higher layer weights are usually obtained with immersion processes. Depending on the type of application and depending on the substrate, the required treatment times are between 15 seconds and 10 minutes, but in practice Treatment times rarely fell below 60 seconds and 5 minutes rarely be exceeded.

Accordingly, the invention also relates to a method for phosphating metal surfaces, preferably surfaces made of steel, zinc, aluminum or alloys, the main component of which is at least one of the metals iron, zinc or aluminum, by treating the surfaces with the solutions described above, preferably with a Temperature between 30 and 70 ° C, for a time between 15 seconds and 10 minutes, preferably one to 5 minutes, by immersion in the solution and / or by spraying with the solution. The process parameters are preferably chosen so that phosphate layers with a layer weight in the range of 0.2 to 1 g / m ² , preferably 0.4 to 0.9 g / m ² and in particular 0.4 to 0.7 g / m ² are obtained will.

The method can be used in particular for the pretreatment of metal surfaces before applying an organic coating, preferably selected from the group of paints and varnishes and the natural or synthetic rubbers and rubbers.

The ready-to-use phosphating solutions can be achieved by dissolving the individual Components in the required concentration in water on site getting produced. However, the usual procedure is to concentrate who manufactures phosphating solutions based on the application concentration be diluted. Aqueous concentrates are usually made so that the application concentration by dilution with water by a factor between 5 and 200, preferably between 20 and 100, can be adjusted. Accordingly, the invention also includes aqueous concentrates, from which the above by appropriate dilution with water described phosphating solutions can be obtained.

As an alternative to liquid-aqueous concentrates, powdered concentrates can be used are used. Their composition is chosen so that when dissolving the powder in water in a concentration between 0.2 and 5 wt .-%, preferably between 0.5 and 3 wt .-% of those described above Receives phosphating solutions.

Iron phosphating baths can be based on the pH value, the electrical conductivity or controlled and regulated via the total acid score will.

To increase the corrosion protection of iron phosphate layers these are subjected to a passivating aftertreatment. Stand for it Chromium-containing and chromium-free post-passivation agents available. The prerequisite for good quality of the subsequent painting is thorough rinsing of the phosphated parts, regardless of whether they were passivated or not. For this, the parts are made once or twice rinsed with process water and finally with deionized water.

Examples

1. alkalische Reinigung (Spritzen)
Ridoline^R 1250 E (Henkel KGaA), 70 °C, 2 min, 1 bar, 20 g/l

2. Spülen

3. Eisenphosphatierung (Spritzen)
50 °C, 2,5 min, 1 bar
Badzusammensetzung: siehe Einzelbeispiele

4. Spülen

5. Spülen, vollentsalztes Wasser

6. Trocknen

7. Für Korrosionsprüfung: Pulverbeschichten mit Pulverlack PE/EP 400 der Fa. Herberts, 10 min bei 180 °C gehärtet.

To check the phosphating baths, steel sheets (St1405) were treated according to the following procedure:

1. alkaline cleaning (spraying)
Ridoline ^R 1250 E (Henkel KGaA), 70 ° C, 2 min, 1 bar, 20 g / l

2. Rinse

3. Iron phosphating (spraying)
50 ° C, 2.5 min, 1 bar
Bath composition: see individual examples

4. Rinse

5. Rinse, demineralized water

6. Drying

7. For corrosion testing: powder coating with powder coating PE / EP 400 from Herberts, hardened at 180 ° C for 10 min.

Layer weights were obtained by peeling off the phosphate layer with triethanolamine determined according to DIN 50942. For testing the corrosion resistance a three-week salt spray test was carried out in accordance with DIN 53167. Here was the paint infiltration on a cut after 21 days of testing measured.

Examples 1 to 4, Comparative Examples 1 to 5

0,79 % H₃PO₄, 85 %

0,38 % NaOH, 50 %

0,014 % Na-Gluconat

0,005 % FeSO₄ x 7 H₂O

The phosphating baths had the following composition:

0.79% H ₃ PO ₄ , 85%

0.38% NaOH, 50%

0.014% Na gluconate

0.005% FeSO ₄ x 7 H ₂ O

Accelerator according to table 1

After adding the accelerator, the pH was adjusted with 50% sodium hydroxide solution set to the value specified in Tab. 1.

Examples 5 to 8

400 ppm m-Nitrobenzolsulfonsäure

240 ppm Milchsäure

125 ppm Gluconsäure

10 ppm Eisen(II)

The phosphating baths had the composition

400 ppm m-nitrobenzenesulfonic acid

240 ppm lactic acid

125 ppm gluconic acid

10 ppm iron (II)

Phosphoric acid, sodium hydroxide solution: Table 2; pH: 4.5

Variation von Phosphat und Gesamtsäure Versuch-Nr. H₃PO₄ 85%ig g/l NaOH 50%ig g/l GS Schichtgew. g/m² Aussehen Beisp.5 4,6 2,2 2,5 0,77 graublau, fest Beisp.6 7,9 3,8 3,7 0,84 bläulich irisierend fest Beisp.7 6,2 3,0 4,2 0,84 bläulich irisierend fest Beisp.8 9,3 4,47 7,2 0,59 grau wenig abwischbar

Variation of phosphate and total acid Trial no. H ₃ PO ₄ 85% g / l NaOH 50% g / l GS Layer weight g / m ² Appearance Ex. 5 4.6 2.2 2.5 0.77 gray-blue, firm Ex. 6 7.9 3.8 3.7 0.84 bluish iridescent tight Ex. 7 6.2 3.0 4.2 0.84 bluish iridescent tight Ex. 8 9.3 4.47 7.2 0.59 gray little wipeable

Examples 9 to 12, Comparative Examples 6 to 8

The phosphating baths had the following composition: 0.5% Phosphoric acid 75% 0.02% 50% gluconic acid 0.1% Na cumene sulfonate 0.1% P3-Tensopon ^R 0555 (nonionic surfactant mixture based on fatty alcohol ethoxylate propoxylate, 30% aqueous solution; Henkel KGaA, Düsseldorf) 0.005% FeSO ₄ x 7H ₂ O

Accelerator according to table 3
adjusted to pH = 5.0 with 50% sodium hydroxide solution.

The coating and testing was carried out as in Examples 1 to 3. The coating thickness was approximately 50 μm. Results are shown in Table 3. Accelerators and phosphating results Trial no. accelerator Layer weight g / m ² Paint infiltration, mm Compare 6 300 ppm NBS 200 ppm hydroxylamine 0.64 2.1 Compare 7 300 ppm NBS 0.61 5.5 Compare 8 400 ppm NBS 0.64 6.5 Ex. 9 300 ppm NBS 0.56 2.1 300 ppm glycine Ex. 10 400 ppm NBS 0.58 1.7 200 ppm glycine Ex. 11 300 ppm NBS 200 ppm lactic acid 0.56 1.9 Ex. 12 300 ppm NBS 300 ppm lactic acid 0.58 1.7

Claims (12)

1. An aqueous solution for the iron phosphating of metals with a pH value of 3.5 to 6 containing

   a) 1 to 20 g/l of dissolved phosphate,

   b) 0.02 to 2 g/l of nitrobenzene sulfonic acid,

   c) water and, if desired, other auxiliaries,

   characterized in that the solution additionally contains

   d) 0.01 to 0.8 g/l of one or more organic monocarboxylic acids corresponding to general formula (I):

   

   in which

   R = H, CH₃, CH₂Y, C₂H₅, C₂H₄Y, C₆H₅, C₆H₄Y or C₆H₃Y₂,

   X and Y independently of one another represent NH₂ or OH and

   n = 0, 1 or 2.
2. A phosphating solution as claimed in claim 1, characterized in that, in general formula (I), n = 0 and X = NH₂.
3. A phosphating solution as claimed in claim 1, characterized in that, in general formula (I) X = OH.
4. A phosphating solution as claimed in one or more of claims 1 to 3, characterized in that it contains 0.1 to 0.8 g/l of one or more carboxylic acids corresponding to general formula (I).
5. A phosphating solution as claimed in one or more of claims 1 to 4, characterized in that it contains 0.2 to 0.5 g/l of nitrobenzene sulfonic acid.
6. A phosphating solution as claimed in one or more of claims 1 to 5, characterized in that it contains m-nitrobenzene sulfonic acid as the nitrobenzene sulfonic acid.
7. A phosphating solution as claimed in one or more of claims 1 to 6, characterized in that it contains one or more of the following auxiliaries:

   e) 0.05 to 3 g/l of free and/or complexed fluoride,

   f) 0.1 to 6 g/l of a chelating carboxylic acid containing at least 4 carbon atoms and at least 3 substituents selected from carboxyl and hydroxy groups,

   g) 0.02 to 20 mmoles/l of molybdate and/or tungstate,

   h) 0.05 to 0.2 g/l of an anionic titanium compound,

   i) up to 40 g/l of surfactants,

   k) 0.05 to 5 g/l of nitrate.
8. A process for the iron phosphating of metal surfaces selected from surfaces of steel, zinc, aluminium or alloys of which the main component is at least one of the metals iron, zinc or aluminium, characterized in that the surfaces are contacted with solutions according to one or more of claims 1 to 7 at a temperature of 30 to 70°C for between 15 seconds and 10 minutes by immersion in and/or spraying with the solution.
9. A process as claimed in claim 8, characterized in that phosphate layers are produced with a layer weight of 0.2 to 1 g/m2.
10. A process as claimed in one or both of claims 8 and 9 for pretreating metal surfaces before the application of an organic coating.
11. An aqueous concentrate which forms an iron phosphating solution according to one or more of claims 1 to 7 by dilution with water by a factor of 5 to 200.
12. A powder which forms an iron phosphating solution according to one or more of claims 1 to 7 by dissolution in water in a concentration of 0.2 to 5% by weight.