PROCESS FOR COATING METALLIC SURFACES WITH A PASSIVATING AGENT, THE PASSIVATING AGENT AND ITS USE

Abstract

The invention relates to a process for coating metal surfaces with an aqueous composition in the form of a solution or in the form of a dispersion, the composition comprising at least one phosphate, at least 3 g/l of at least one titanium or/and zirconium compound and at least one complexing agent, and also to corresponding aqueous compositions. The coatings prepared thereby have very good bare corrosion protection in the NSS salt spray test and in the condensation-water/constant-climate test

Claims

1. A process for coating and passivating metal surfaces with an aqueous composition in the form of a solution or in the form of a dispersion, wherein the composition comprises 12 to 400 g/L of at least one phosphate, 3 to 200 g/L of at least one titanium or zirconium compound, 1 to 200 g/L of at least one complexing agent, selected from the group of compounds based on phosphonic acid, phytin and tannin, wherein content of compounds based on phosphonic acid amounts to 0 or 1 to 200 g/L, and wherein the content of compounds based on phytin or tannin amounts to 0 or 0.05 to 30 g/L, and also 3 to 100 g/L of cations of aluminum, chromium(III) or zinc or at least one compound having a content of aluminum, chromium(III) or zinc in the range from 1 to 100 g/L, calculated as metal, wherein the content of zinc is at least 3 g/L, in that the composition has values of the free acid FA in the range from 2 to 25 points, values of total acid TA in the range from 20 to 45 points, and values of total acid Fischer TAF in the range from 12 to 20 points, and in that a wet film of the aqueous composition is dried on metal strips or sheets without the wet film or the dried film being rinsed with water.

2. The process according to claim 1, wherein the composition further comprises cations of iron or manganese or at least one compound having a content of iron or manganese.

3. The process according to claim 1, wherein the composition comprises a total content of cations of aluminum, chromium(III), iron, manganese or zinc or of at least one compound having a content of aluminum, chromium(III), iron, manganese or zinc in the range from 3 to 100 g/L, calculated as metal.

4. The process according to claim 1, wherein the composition substantially contains only cations of aluminum, iron, manganese, titanium, zinc or zirconium.

5. The process according to claim 1, wherein the composition comprises a total content of at least one titanium or zirconium compound based on complex fluoride in the range from 1 to 200 g/L.

6. The process according to claim 1, wherein the composition comprises a content of free fluoride F.sub.free in the range from 0.01 to 5 g/L or a content of total fluoride F.sub.total in the range from 3 to 180 g/L.

7. The process according to claim 1, wherein the composition further comprises at least one silane/silanol/siloxane/polysiloxane.

8. The process according to claim 7, wherein the composition contains a content of at least one silane/silanol/siloxane/polysiloxane in the range from 0.1 to 200 g/L, calculated on the basis of silane or polysiloxane in the particular starting compound in question.

9. The process according to claim 1, wherein the composition further comprises at least one additive selected from the group consisting of a wetting agent, a demulsifying agent, an emulsifier, an antifoam, a corrosion inhibitor, and a wax.

10. The process according to claim 1, wherein the composition has a pH value in the range from 0 to 10.

11. A process according to claim 1, wherein the metal surface treated with the aqueous composition is a metal surface comprising at least one member selected from the group consisting of aluminum, iron, magnesium, titanium, zinc, and tin, in strips or sheets.

12. A coating prepared by the process according to claim 1.

13. A metal component coated by the process according to claim 1.

14. A motor vehicle comprising the metal component of claim 13.

15. An architectural element comprising the metal component of claim 13.

16. A domestic appliance coated by the process according to claim 1.

Description

EXAMPLES AND COMPARATIVE EXAMPLES

[0098] The Examples (E) and Comparative examples (CE) described hereinbelow are intended to explain the subject-matter of the invention in detail.

Comparative Example CE 0

[0099] Hot-dip galvanised sheets were coated in a laboratory rollcoater with aqueous solutions that contained only an addition of zinc dihydrogen phosphate (60%) in the range from 40 to 100 g/l and a corresponding molar amount of orthophosphoric acid in demineralised water. Coatings having a layer weight of from 110 to 360 mg/m.sup.2 P.sub.2O.sub.5 were obtained. In the neutral salt spray test (NSS test) according to DIN EN ISO 9227 (bare corrosion test), the coatings exhibited corrosion phenomena of from 1 to 5% by surface area after only about 1 hour and thick, white layers of zinc corrosion products over the entire surface after only 8 hours. In the condensation-water/constant-climate test according to DIN EN ISO 6270-2 (KK test), white rust of up to 10% by surface area was found after 2 days. Such coatings are unusable for any purpose in European industry.

Example E 0 According to the Invention

[0100] In comparison therewith, an aqueous solution having an addition of zinc dihydrogen phosphate (60%) in the range from 40 to 60 g/l, with an addition of a corresponding molar amount of orthophosphoric acid, of 25 g/l of H.sub.2TiF.sub.6 (50%), of 6 g/l of γ-APS (γ-aminopropyltriethoxysilane) and with demineralised water as the remainder was used for coating hot-dip galvanised sheets by roll coating in the laboratory. Coatings of in each case approximately from 110 to 165 mg/m.sup.2 P.sub.2O.sub.5, 36 mg/m.sup.2 Ti and 6 mg/m.sup.2 Si were obtained. In the neutral salt spray test (NSS test) according to DIN EN ISO 9227 (bare corrosion test), these coatings exhibited a corrosive attack of from 1 to 5% by surface area, based on the entire surface, only after 48 to 72 hours, although there was no chromium in the coating. For high demands in European industry, resistances in the NSS test of 2 days, rarely of 3 or 4 days, with corrosion phenomena ≦5% by surface area are nowadays required. Such bare corrosion resistance is usually achieved only with chromium-rich systems. With the process according to the invention, bare corrosion resistances of 2 to 5 days were achieved, the substrates and the compositions being varied. In the condensation-water/constant-climate test according.to DIN EN ISO 6270-2 (KK test), the improvement compared with Comparative example CE 0 is markedly smaller, however, than in the neutral salt spray test (NSS test). Even after 10 days' KK test, no rust deposit had yet formed.

Examples E 1 to E 44 According to the Invention and Comparative Examples CE 1 to CE 4

[0101] Aqueous compositions were mixed, the compositions of which are shown in Table 1 as concentrates. The dilution factor shows the dilution to the bath concentration used, that is to say from a concentrate to a bath, so that in the case of a concentrate 200 g, for example, were used and were diluted to 1000 g with water using a dilution factor of 5. Aluminium was used in the form of monoaluminium phosphate, chromium in the form of complexed chromium(III) fluoride or/and chromium(III) phosphonate, iron in the form of iron(III) nitrate hydrate, manganese in the form of manganese carbonate or/and manganese oxide, zinc in the form of monozinc phosphate or/and zinc oxide. As silanes there were added as No. 1) 3-aminopropyltriethoxysilane (APS), as No. 2) N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPS) and as No. 3) tetraethoxysilane (TEOS). As complexing agents there were used as No. 1) 1-hydroxyethane-1,1-diphosphonic acid (HEDP) and as No. 2) phytic acid. As inhibitors there were added as No. 1) polymeric quatemary ammonium salt, as No. 2) quatemary ammonium salt, as No. 3) polyvinylpyrrolidone and as No. 4) tetraethanolamine. As titanium or/and zirconium compound there were added hexafluorotitanic acid, hexafluorozirconic acid or dihydroxo-bis-(ammonium lactate) titanate. As wax there was used a wax emulsion based on oxidised polyethylene. The pH value was adjusted, where appropriate, using aqueous ammonia solution. The ranges indicated for the pH value apply both to concentrates and to bath concentrations. When diluting the concentrates to prepare bath solutions, care was taken to ensure that no precipitates formed. The concentrates and bath solutions were stored at room temperature for from one to 24 hours before they were used.

[0102] There were then used in each case at least 9 sheets of hot-dip galvanised (HDG) steel in Examples E 1 to E 26 and E 36 to E 44 as well as in Comparative examples CE 1 to CE 4, sheets of Galvalume® (AZ) in Examples E 27 to E 32, sheets of Galfan® (ZA) in Example E 33 and sheets of Alusi® (AS) in Examples E 34 and E 35.

[0103] The sheets were pre-cleaned with a cloth in order largely to remove adherent anticorrosive oil and in order to achieve uniform distribution of the oil or other impurities. The sheets were then cleaned by spraying with a mildly alkaline, silicate-free powder cleaner until complete wettability with water was present. The duration for this was generally from 20 to 30 seconds. Rinsing with tap water by immersion was then carried out, followed by rinsing with tap water by spraying for 6 seconds and rinsing with demineralised water for 6 seconds. The majority of the adherent water was then removed from the sheets by squeezing between two rubber rollers. The sheets were then blown dry with oil-free compressed air.

[0104] The dry sheets were brought into contact with the aqueous composition at about 25° C. with the aid of a laboratory rollcoater. The pH value of the compositions was determined with pH indicator paper. A wet film having a thickness of approximately from 9 to 10 μm was applied. A dry film having a thickness of from 0.2 to 0.6 μm was produced by drying the wet film. To this end, the sheets so treated were dried at approximately 40 or 65° C. PMT. The edges of the coated sheets were then masked with commercial adhesive tape in order to rule out edge effects during the corrosion testing.

[0105] The coated sheets were then tested for their bare corrosion protection in the condensation-water/constant-climate test (KK test) according to DIN EN ISO 6270-2 and in the neutral salt spray test (NSS test) according to DIN EN ISO 9227. Evaluation was made visually. The indicated values for the corrosion correspond to the percentage surface area, which corresponds to the entire area (100%) accessible to chemical loading. In the case of Galvalume® sheets, “black rust” and “white rust” were evaluated in total. The results of the corrosion tests show the range of the corrosion protection, all the measured results, including measured values which are to be regarded as freak values, being used.

[0106] In Comparative examples CE 5 to CE 7, electrolytically galvanised sheets (ZE) were brought into contact with typical zinc-containing phosphating solutions after previous mildly alkaline cleaning, rinsing with tap water and titanium-phosphate-containing activation. The phosphation took place in Comparative examples CE 5 and CE 6 at temperatures in the range from room temperature to 40° C. by spraying and rinsing (rinse process), in Comparative example CE 7 at from 55 to 60° C. by rolling and drying (no-rinse process). The former were also oiled or subjected to post-rinsing.

TABLE-US-00001 TABLE 1 Overview of the compositions of the solutions used and their composition as well as the properties of coatings prepared therewith as well as corresponding compositions for comparison Contents in g/l E 1 E 2 E 3 E 4 E 5 E 6 E 7 E 8 E 9 E 10 Substrate HDG HDG HDG HDG HDG HDG HDG HDG HDG HDG Zn 6.4 12.8 12.8 19.1 19.1 19.1 12.8 12.8 57.1 57.1 Al 7.4 4.9 4.9 2.4 2.4 2.4 — — — — PO.sub.4 105.8 107.5 107.5 109.3 109.3 109.3 55.4 55.4 248.8 248.8 P.sub.2O.sub.5 79.1 80.4 80.4 81.7 81.7 81.7 41.4 41.4 185.9 185.9 H.sub.2TiF.sub.6 72.5 72.5 72.5 72.5 72.5 72.5 72.5 72.5 162.5 162.5 Ti 21.2 21.2 21.2 21.2 21.2 21.2 21.2 21.2 47.5 47.5 F.sub.total 50.4 50.4 50.4 50.4 50.4 50.4 50.4 50.4 113.0 113.0 Complexing agent No., g/l 1) 69.6 1) 34.8 1) 69.6 1) 69.6 1) 34.8 1) 21.9 1) 34.8 1) 34.8 1) 78.0 1) 78.0  Silane No., g/l 1) 34.8 1) 34.8 1) 34.8 1) 34.8 1) 34.8 1) 34.8 1) 34.8 1) 34.8 1) 78.0 1) 156.0 NH.sub.3 — — — — — — — 17.4 45.6 35.1 Dilution factor 5 5 5 5 5 5 5  5  10 10 pH value 0.5-1 0.5-1 0.5-1 0.5-1 0.5-1 0.5-1 0.5-1 2.2-2.5 1.9-2.2 1.9-2.2 Layer weight mg/m.sup.2: Si 6 6 6 6 6 6 6  6  6 12 Ti 37 39 36 37 36 36 37   34   34 33 P.sub.2O.sub.5 225 190 220 220 175 155 96   100   170 165 KK test 10 days   0%   0%   0%   0%   0%   0% — — — — KK test 20 days — — — — — — 70-90%  5-15%   0%   0% Salt spray test 3 days <5-10% <5-15%  1-10% <1-5% <1-10%  <1-1% — — — <5-15% Salt spray test 4 days  5-10% <5-20% <5-10% 1-10% <1-15% <1-<5% 10-20% <5-80% <5-20% — Contents in g/l E 11 E 12 E 13 E 14 E 15 E 16 E 17 E 18 E 19 E 20 Substrate HDG HDG HDG HDG HDG HDG HDG HDG HDG HDG Zn 57.1 25.5 38.2 25.5 25.5 25.5 25.5 25.5 25.5 25.5 Mn — — — 5.6 4.2 — — — — — PO.sub.4 248.8 111.0 166.5 111.0 111.0 111.0 111.0 111.0 111.0 111.0 P.sub.2O.sub.5 185.9 82.9 124.4 82.9 82.9 82.9 82.9 82.9 82.9 82.9 H.sub.2TiF.sub.6 130 72.5 72.5 58.0 72.5 — 72.5 72.5 72.5 72.5 H.sub.2ZrF.sub.6 — — — — — 40.6 — — — — Ti or Zr 38.0 21.2 21.2 16.9 21.2 18.3 21.2 21.2 21.2 21.2 F.sub.total 90.4 50.4 50.4 40.4 50.4 22.3 50.4 50.4 50.4 50.4 Complexing agent No., g/l — 1) 34.8 1) 34.8 1) 17.4 1) 34.8 1) 34.8 1) 34.8 1) 34.8 1) 34.8 1) 34.8 Complexing agent No., g/l 2) 104.0 — — 2) 46.4 — — — — — — Silane No., g/l 1) 52.0  3) 33.1 2. 34.8 1) 34.8 1) 34.8 1) 34.8 1) 34.8 1) 69.6 1) 69.6 1) 69.6 NH.sub.3 — — — — — — — 17.4 17.4 17.4 Corrosion inhibitor No., g/l — — — — — — —  1) 116.0  2) 116.0  3) 116.0 Dilution factor 10 5 5 5 5 5 5 5 5 5 pH value 0.5-1 0.5-1 0.5-1 ca. 1.5 ca. 1.5 0.5-1 0.5-1 1.9-2.2 1.9-2.2 1.9-2.2 Layer weight mg/m.sup.2: Mn — — — 44 35 — — — — — Si 4 6 6 6 6 6 6 14 19 12 Ti or Zr 28 34 36 28 35 33 36 37 50 36 P.sub.2O.sub.5 186 160 295 196 166 144 164 194 260 190 KK test 10 days   0%   1%   0%   0%   0%    1% — — — — KK test 20 days — — — — — — <1%   0%  0%   0% Salt spray test 3 days 40-60% 15-20% — —  5-10% 70-100% — — — — Salt spray test 4 days — — 10-20% 20-40% 15-25% — <5% 0-<5% 0-1% 0-<5% Contents in g/l E 21 E 22 E 23 E 24 E 25 E 26 E 27 E 28 E 29 E 30 Substrate HDG HDG HDG HDG HDG HDG AZ AZ AZ AZ Zn 25.5 25.5 25.5 25.5 25.5 — 25.5 38.2 38.2 25.5 Mn — — — — 13.8 — — — — — Fe — — — — — 13.0 — — — — Cr — — — 13.7 13.7 — — — — — PO.sub.4 111.0 111.0 111.0 139.9 132.8 240.3 111.0 166.5 166.5 111.0 P.sub.2O.sub.5 82.9 82.9 82.9 104.6 99.2 179.6 82.9 124.4 124.4 82.9 H.sub.2TiF.sub.6 72.5 72.5 72.5 72.5 72.5 162.5 72.5 72.5 72.5 72.5 Ti 21.2 21.2 21.2 21.2 21.2 47.5 21.2 21.2 21.2 21.2 F.sub.total 50.4 50.4 50.4 50.4 50.4 113.0 50.4 50.4 50.4 50.4 Complexing agent no., g/l 1) 34.8 1) 34.8 1) 34.8 1) 42.5 1) 34.8 1) 69.6 1) 34.8 1) 34.8 1) 34.8 1) 34.8 Complexing agent No., g/l — — — — — — — — 2) 34.8 — Silane No., g/l 1) 34.8 1) 69.6 1) 34.8 1) 69.6 1) 69.6 1) 78.0 1) 34.8 1) 69.6 1) 69.6 — NH.sub.3 — 17.4 26.1 17.4 17.4 — 21.8 20.9 21.8 23.1 Wax — — 17.4 — — — — — — — Tannin — 5.0 — — — — — — — — Corrosion inhibitor No., g/l  4) 111.0 — — — — — — — — Dilution factor 5 5 5 5 5 10 5 5 5 5 pH value 1.9-2.2 1.9-2.2 2.2-2.5 1.9-2.2 1.9-2.2 0.5-1.0 1.9-2.2 1.9-2.2 1.9-2.2 1.9-2.2 Layer weight mg/m.sup.2: Si 6 13 8 13 12 6 8 8 12 — Ti 33 32 41 38 37 42 42 40 38 37 Cr — — — 32 32 — — — — — P.sub.2O.sub.5 154 168 205 235 210 175 150 255 290 180 KK test 10 days — — — — —  5-10% — — — — KK test 20 days   100%  0-25% <1-1% 0%   0% —   0%   0%  0% 1-<5% Salt spray test 3 days <5-<10% — — — — <5-40% — — — Salt spray test 4 days — <1-<5% 1-20% — — — — — —  <1% Salt spray test 7 days — — — 0% 0-<5% — <1-<5% — —  1-5% Salt spray test 10 days — — — 0% 0-20% — — <1-<5% <1% — Contents in g/l E 31 E 32 E 33 E 34 E 35 E 36 E 37 E 38 E 39 E 40 Substrate AZ AZ ZA Alusi Alusi HDG HDG HDG HDG HDG Zn 57.1 57.1 25.5 25.5 12.7 49.9 49.9 38.2 25.5 25.5 PO.sub.4 248.8 248.8 111.0 111.0 55.5 217.6 217.6 166.5 111.0 111.0 P.sub.2O.sub.5 185.9 185.9 82.9 82.9 41.5 162.6 162.6 124.4 82.9 82.9 H.sub.2TiF.sub.6 162.5 195.0 101.5 72.5 72.5 162.5 162.5 14.5 43.5 87.0 Ti 47.5 57.0 29.7 21.2 21.2 47.5 47.5 4.2 12.7 25.4 F.sub.total 113.0 135.6 70.6 50.4 50.4 113.0 113.0 10.1 30.3 60.6 Complexing agent No., g/1 1) 78.0 1) 78.0 1) 34.8 1) 34.8 1) 34.8 1) 117.0 1) 117.0 1) 34.8 1) 34.8 1) 34.8 Silane No., g/l — — 1) 69.6 1) 34.8 1) 34.8 1) 78.0  — 1) 34.8 1) 34.8 1) 34.8 NH.sub.3 51.8 62.0 23.5 26.1 21.8 52.7 59.7 — — — Dilution factor 10 10 5 5 5 10 10 5 5 5 pH value 1.9-2.2 1.9-2.2 1.9-2.2 2.2-2.5 1.9-2.2 1.9-2.2 1.9-2.2 0.5-1 0.5-1 0.5-1 Layer weight mg/m.sup.2: Si — — 13 n.b. n.b. 6 — 6 6 6 Ti 35 36 48 n.b. n.b. 35 35 6 20 42 P.sub.2O.sub.5 168 185 170 n.b. n.b. 180 180 185 158 160 KK test 10 days — — — — — — —   <5%   0%   0% KK test 20 days <5%   <5% <1%   0%  0-15% 15-25%   0-1% — — — Salt spray test 3 days — — — 10-20% 20-50% <5-50% 60-100% 70-90% — <5-10% Salt spray test 4 days <1%  <1-1% <5%   20% 20-50% — — — 15-40% <5-15% Salt spray test 7 days <5-5%  <1-<5% — — — — — — — — Contents in g/l E 41 E 42 E 43 E 44 CE 1 CE 2 CE 3 CE 4 Substrate HDG HDG HDG HDG HDG HDG HDG HDG Zn 85.7 25.5 — — 63.7 38.2 25.5 25.5 Al — — 9.85 9.85 — — — — PO.sub.4 373.1 111.0 104.0 104.0 231.2 166.5 111.0 111.0 P.sub.2O.sub.5 278.9 82.9 77.7 77.7 172.8 124.4 82.9 82.9 Ti chelate — 107.3 — — — — — — H.sub.2TiF.sub.6 162.5 — 72.5 72.5 — 72.5 72.5 58.0 Ti 47.5 17.5 21.2 21.2 — 21.2 21.2 16.9 F.sub.total 113.0 — 50.4 50.4 — 50.4 50.4 40.3 Complexing agent No., g/l 2) 104.0 1) 69.6 1) 69.6 1) 69.6 2) 69.6 — — — Complexing agent No., g/l — — — 2) 69.6 — — — — Silane No., g/l — — 1) 34.8 1) 34.8 — 1) 34.8 — — Wetting agent — 0.3 — — — — — — Dilution factor 10 5 5 5 5 5 5 5 pH value 0.5-1 ca. 2 0.5-1 0.5-1 0.5-1 0.5-1 0.5-1 0.5-1 Layer weight mg/m.sup.2: Si — — 6 6 — 6 — — Ti 32 35 36 36 — 32 32 27 P.sub.2O.sub.5 225 270 225 245 240 165 115 105 KK test 10 days   0% —   0%   0%  <5%   0%   1%   30% KK test 20 days —   <1% — — — — — — Salt spray test 3 days 10-40% 10-30% — <5-10% 100% 5-10% 10-30% 60-70% Salt spray test 4 days — — <5-10% — — — — — Contents in g/l; zinc phosphations CE 5 CE 6 CE 7** Substrate ZE ZE ZE Zn 1.6 1.6 1.7 PO.sub.4 18.1 18.1 10.3 P.sub.2O.sub.5 13.5 13.5 7.7 Ti, Zr, silane, polysiloxane 0 0 0 in each case F.sub.total, complexing agent 0 0 0 in each case Mn 1.9 1.9 0.85 Ni 1.3 1.3 0.31 Layer weight g/m.sup.2 1.8 1.8 0.3 After-treatment, post-rinsing oiled Zr rinsing none Zr layer calculated as metal mg/m.sup.2 — 9 — KK test 1 day —  1% WR 40-50% WR KK test 2 days — <5% WR — KK test 21 days <1% WR — — Salt spray test 1 day 5-10% WR  20% WR  100% WR Salt spray test 2 days 20% WR 50-60% WR   — Salt spray test 3 days 40% WR — — **= microphosphation WR = white rust

TABLE-US-00002 TABLE 2 Examples of acidities in compositions based, for example, on E 10 with a reduced silane addition and measured after dilution to 60 g/l A B C pH value ca. 0.5 ca. 2 ca. 3 Free acid (FA) 18.0 9.9 5.3 Total acid (TA) 38.8 31.5 25.6 Total acid.sub.Fischer (TAF) 17.6 16.4 15.3 S value (FA:TA) 0.46 0.31 0.21 S value (FA:TAF) 1.02 0.60 0.35

[0107] The coatings prepared according to the invention exhibited a layer weight in the range from 350 to 650 mg/m.sup.2 total coating and a layer thickness approximately in the range from 0.2 to 0.6 μm. They were so thin and were produced so quickly that the substances are not present in sufficiently crystalline form in the coatings that they can be determined by radioscopy. Scanning electron microscope photographs of these coatings substantially show the topography of the cleaned metal substrate surface. The applied coatings according to the invention are not shown significantly topographically under the scanning electron microscope. The coatings are evidently homogeneous transparent layers. Depending on the substrate type and coating, they render the metal surface slightly matt, equally as well as without a coating, or with a more pronounced gloss. In most cases the coatings do not have a tinge of colour.

[0108] In a further series, a powder coating based on polyester was applied in a layer thickness of approximately 80 μm to the hot-dip galvanised and pretreated sheets based on the composition of E 10. In the subsequent cross-cut test of the painted sheets according to DIN EN ISO 2409, a value of Gt 0 was always obtained before the corrosive action.

[0109] In each of Examples E 1 to E 6, the compositions comprise aluminium and zinc, the contents of which were varied. The KK test over 10 days on the associated coatings was without problems. In the case of Examples E7 to E 13, which comprise only zinc as cation, the PO.sub.4 content, Ti content, pH value, type of complexing agent and type of silane in particular were varied. The corrosion protection can decrease at a lower phosphate content. Complexing agent 1) performed better than complexing agent 2). Silanes 1) and 2) performed slightly better than silane 3). In Examples E 14 and E 15, zinc and manganese were chosen as cations. It should be ensured in this connection that the manganese content does not impair the corrosion protection. In Examples E 16 and E 17, the addition of a titanium compound is compared with the addition of a zirconium compound. The addition of a titanium compound permits markedly higher corrosion protection on hot-dip galvanised surfaces. In Examples E 18 to E 21, various corrosion inhibitors were additionally used. The corrosion inhibitors improve the corrosion protection, corrosion inhibitor 4) having a slightly less protective action. The addition of tannin in Example E 22 did not bring about a significant improvement. In Examples E 23 to E 26, the additions of cations were varied. The addition of chromium(III) improved the corrosion protection very considerably. The use of only iron cations was less successful for the corrosion protection. In Examples E 27 to E 32 on Galvalume®, outstanding corrosion protection was found. A silane addition is not necessary for Galvalume® surfaces but is advantageous for a high degree of corrosion protection. Example E 33 demonstrates that good corrosion protection results can also be achieved on Galfan® surfaces. In Examples E 34 and E 35 for Alusi® surfaces, it must be ensured that the cation and phosphate content is not too low. In Examples E 36 to E 44, hot-dip galvanised surfaces were again coated. In Examples E 36 to E 41, the operation was carried out with or without silane and with varying contents of titanium compound. Better corrosion protection was obtained with the addition of silane or with an increased content of titanium compound. Complexing agent 1) usually performs better than complexing agent 2). Replacing titanium complex fluoride by a titanium chelate in Example E 42 resulted in outstanding corrosion protection for a silane-free and fluoride-free composition. In Examples E 43 and E 44, only aluminium was used as cation. The associated coatings appeared slightly matt. The corrosion protection was good.

[0110] The bare corrosion protection of the examples according to the invention, determined in the NSS test, is in most cases better by at least a time factor of 20 or 30 than that of comparable zinc-phosphated coatings. The main reason for this is assumed to be that the coating according to the invention is unusually closed and pore-free.