Process for coating metallic surfaces with a multicomponent aqueous composition

Abstract

The invention relates to a process for coating metallic surfaces with a composition containing silane/silanol/siloxane/polysiloxane, wherein, in addition to a) at least one compound selected from silanes, silanols, siloxanes and polysiloxanes, b) at least one compound containing titanium, hafnium, zirconium, aluminium and/or boron, and c) at least one type of cation selected from cations of metals of subgroups 1 to 3 and 5 to 8, including lanthanides, and of main group 2 of the periodic table of the elements, and/or at least one corresponding compound,
the composition contains at least one substance d) selected from: d.sub.1) silicon-free compounds having at least one amino, urea and/or ureido group in each case, d.sub.2) anions of nitrite and/or compounds having at least one nitro group, d.sub.3) compounds based on peroxide, and d.sub.4) phosphorus-containing compounds, anions of at least one phosphate and/or anions of at least one phosphonate, as well as e) water, and f) optionally also at least one organic solvent. The invention further relates to corresponding aqueous compositions.

Claims

1. A process consisting of coating a metallic surface with a coating composition consisting of: a) at least one silicon containing silane compound selected from the group consisting of: i) an amino-functional trialkoxysilane with one amino group per molecule; ii) a silane having one terminal amino group and one ureido group per molecule; iii) a bis-trialkoxysilane; and iv) any combination thereof, wherein the composition has a combined content of i), ii), iii), and iv) which ranges from 0.02 to 1 g/L, calculated on the basis of the corresponding silanes; b) at least two different complex fluorides selected from the group consisting of complex fluorides of titanium, complex fluorides of hafnium, complex fluorides of zirconium, complex fluorides of aluminum, and complex fluorides of boron; and c) at least one cation selected from cerium, chromium, iron, calcium, cobalt, copper, magnesium, manganese, molybdenum, nickel, niobium, tantalum, yttrium, zinc, tin and other lanthanides, wherein the content of cations or corresponding compound c) ranges from 0.01 to 6 g/L; d) at least one substance selected from the group consisting of d.sub.1) from 0.01 to 10 g/L of a silicon-free compound having at least one of an urea or an ureido group; d.sub.2) from 0.01 to 5 g/L of a nitrite compound or a compound having a nitro group; and d.sub.3) from 0.01 to 12 g/L of a phosphonate; e) water; and f) from 20 to 200 g/L of an organic compound, wherein the organic compound is based on at least one member selected from the group consisting of acrylic and urethane; wherein when manganese is present, it has a content of at least 0.08 g/L, or when both manganese and zinc are present, the manganese has a content higher than the zinc content, and wherein the composition has a free fluoride content which ranges from 0.001 to 3 g/L, calculated as F.sup.−.

2. The process according to claim 1, wherein content of complex fluoride ranges from 0.01 to 10 g/L, calculated as the sum of the corresponding metal complex fluorides calculated as MeF.sub.6, wherein Me is a metal.

3. The process according to claim 1, wherein the coating formed has a layer weight, which ranges from 1 to 200 mg/m.sup.2, calculated as elemental titanium, wherein the layer weight is based only on titanium and zirconium.

4. The process according to claim 1, wherein the composition forms a coating with a layer weight which, based only on said silanes, ranges from 0.2 to 1000 mg/m.sup.2, calculated as the corresponding extensively condensed polysiloxane.

5. The process according to claim 1, wherein the composition is free of particles.

6. The process according to claim 1, wherein the coating composition contains each of d.sub.1) the silicon-free compound having at least one of a urea or an ureido group; d.sub.2) the nitrite or compound having a nitro group; and d.sub.3) the phosphonate.

7. The process according to claim 1, wherein the coating composition contains manganese and zinc.

8. The process according to claim 1, wherein the at least two complex fluorides comprise a titanium complex fluoride and a zirconium complex fluoride.

9. A process consisting of coating a metallic surface with a composition, said composition consisting of: a) at least one silicon containing silane compound selected from the group consisting of: i) an amino-functional trialkoxysilane with one amino group per molecule; ii) a silane having one terminal amino group and one ureido group per molecule; iii) a bis-trialkoxysilane; and iv) any combination thereof, wherein the composition has a combined content of i), ii), iii), and iv) which ranges from 0.02 to 1 g/L, calculated on the basis of the corresponding silanes; b) at least two different complex fluorides selected from the group consisting of complex fluorides of titanium, complex fluorides of hafnium, complex fluorides of zirconium, complex fluorides of aluminum, and complex fluorides of boron; and c) at least one cation selected from cerium, chromium, iron, calcium, cobalt, copper, magnesium, manganese, molybdenum, nickel, niobium, tantalum, yttrium, zinc, tin and other lanthanides, wherein the content of cations or corresponding compound c) ranges from 0.01 to 6 g/L; at least one substance d) selected from the group consisting of d.sub.1) from 0.01 to 10 g/L a silicon-free compound having at least one of an urea or an ureido group; d.sub.2) from 0.01 to 5 g/L an anion of nitrite or a compound having at least one nitro group; d.sub.3) from 0.01 to 1 g/L of a compound based on peroxide; and d.sub.4) 0.01 to 12 g/L of a phosphonate; e) water; f) at least one organic compound based on at least one member selected from the group consisting of acrylic and urethane; g) an organic solvent; and at least one member selected from the group consisting of an alkoxide, a carbonate, a chelate, a surfactant, a biocide and a defoamer.

10. The process according to claim 9, wherein the content of complex fluoride ranges from 0.01 to 10 g/L, calculated as the sum of the corresponding metal complex fluorides calculated as MeF.sub.6.

11. The process according to claim 10, wherein the content of complex fluoride is 0.01 g/L.

12. The process according to claim 9, wherein the composition forms a coating having a layer weight which ranges from 1 to 200 mg/m.sup.2, calculated as elemental titanium, wherein the layer weight is based only on titanium and zirconium.

13. The process according to claim 9, wherein the composition forms a coating with a layer weight which, based only on silanes ranges from 0.2 to 1000 mg/m.sup.2, calculated as the corresponding extensively condensed polysiloxane.

14. The process according to claim 9, wherein: the organic solvent is selected from the group consisting of ethanol, methanol, isopropanol and dimethylformamide.

15. The process according to claim 9, wherein the solvent is methanol.

16. The process according to claim 9, wherein the coating composition comprise each of d.sub.1) the at least one of a urea or an ureido group; d.sub.2) the nitrite or compound having a nitro group; d.sub.3) the compound based on peroxide; and d.sub.4) the phosphonate.

17. A process consisting of coating a metallic surface with a coating composition consisting of: a) at least one silicon containing silane compound selected from the group consisting of: i) an amino-functional trialkoxysilane with one amino group per molecule; ii) a silane having one terminal amino group and one ureido group per molecule; iii) a bis-trialkoxysilane; and iv) any combination thereof, wherein the composition has a combined content of i), ii), iii), and iv) which ranges from 0.02 to 1 g/L, calculated on the basis of the corresponding silanes; b) at least two different complex fluorides selected from the group consisting of complex fluorides of titanium, complex fluorides of hafnium, complex fluorides of zirconium, complex fluorides of aluminum, and complex fluorides of boron; c) at least one cation selected from cerium, chromium, iron, calcium, cobalt, copper, magnesium, manganese, molybdenum, nickel, niobium, tantalum, yttrium, zinc, tin and other lanthanides, wherein the content of cations or corresponding compound c) ranges from 0.01 to 6 g/L; at least one substance d) selected from the group consisting of d.sub.1) from 0.01 to 10 g/L of a silicon-free compound having at least one of an urea or an ureido group; and d.sub.2) from 0.01 to 12 g/L of a phosphonate; and e) water; wherein when manganese is present, it has a content of at least 0.08 g/L, or when both manganese and zinc are present, the manganese has a content higher than the zinc content, and wherein the composition has a free fluoride content which ranges from 0.001 to 3 g/L, calculated as F.sup.−.

Description

EXAMPLES AND COMPARATIVE EXAMPLES

(1) The Examples according to the invention (E) and Comparative Examples (CE) described below are intended to illustrate the subject matter of the invention in greater detail.

(2) The aqueous bath compositions are prepared as mixtures according to Table 1 using already prehydrolysed silanes. They each contain predominantly one silane and optionally also have small contents of at least one other similar silane, where here again the word silane is used rather than silane/silanol/siloxane/polysiloxane by way of simplification, and where normally these various compounds, sometimes in a larger number of similar compounds, also pass through into the formation of the coating, so there are often several similar compounds present in the coating as well. Depending on the silane, the prehydrolysis step can also take several days at room temperature, with vigorous stirring, if the silanes to be used are not already present in prehydrolysed form. The prehydrolysis of the silane is carried out by placing the silane in excess water and optionally catalysing with acetic acid. Acetic acid was added in only a few embodiments for the sole purpose of adjusting the pH. In some embodiments, acetic acid is already present as a hydrolysis catalyst. Ethanol is formed in the hydrolysis, but is not added. The finished mixture is used fresh.

(3) Then, for each test, at least 3 sheets of cold-rolled steel (CRS), aluminium alloy Al 6016, steel hot-dip galvanized or electrogalvanized on both sides, or Galvaneal® (ZnFe layer on steel), previously cleaned with an aqueous alkaline cleaner and rinsed with industrial water and then with demineralized water, are brought into contact on both sides with the appropriate pretreatment liquid in Table 1 at 25° C. by spraying, dipping or rollcoater treatment. The sheets treated in this way were then dried at 90° C. PMT and subsequently lacquered with a cathodic automobile dip lacquer (CDL). These sheets were then provided with a complete commercial automotive lacquer system (filler, covering lacquer, transparent lacquer; overall thickness of stacked layers, including CDL, approx. 105 μm) and tested for their corrosion protection and lacquer adhesion. The compositions and properties of the treatment baths and the properties of the coatings are collated in Table 1.

(4) The organofunctional silane A is an amino-functional trialkoxysilane and has one amino group per molecule. Like all the silanes used here, it is in extensively or almost completely hydrolysed form in the aqueous solution. The organofunctional silane B has one terminal amino group and one ureido group per molecule. The non-functional silane C is a bis-trialkoxysilane; the corresponding hydrolysed molecule has up to 6 OH groups on two silicon atoms.

(5) The complex fluorides of aluminium, silicon, titanium or zirconium are used extensively in the form of an MeF.sub.6 complex, but the complex fluorides of boron are used extensively in the form of an MeF.sub.4 complex. Manganese is added to the particular complex fluoride solution as metallic manganese and dissolved therein. This solution is mixed with the aqueous composition. If no complex fluoride is used, manganese nitrate is added. Copper is added as copper(II) nitrate and magnesium as magnesium nitrate. Iron and manganese are mixed in as nitrates. The peroxide was used as dilute hydrogen peroxide. Nitrite is added as sodium nitrite, while nitrate is added as sodium nitrate or nitric acid. Phosphate is used as trisodium orthophosphate hydrate and phosphonate is used as diphosphonic acid with a medium-length alkyl chain in the middle of the molecule.

(6) The silanes present in the aqueous composition—concentrate and/or bath—are monomers, oligomers, polymers, copolymers and/or reaction products with other components due to hydrolysis reactions, condensation reactions and/or other reactions. The reactions take place especially in the solution, during drying or optionally also during curing of the coating, especially at temperatures above 70° C. All the concentrates and baths proved to be stable for one week without undergoing changes or precipitations. No ethanol was added. Ethanol contents in the compositions originated only from chemical reactions.

(7) In the majority of Examples and Comparative Examples, the pH is adjusted with ammonia if at least one complex fluoride is present and with an acid in other cases. All the baths have a good solution quality and almost always a good stability. The bath stability was found to be of limited duration only in E 16. There are no precipitations in the baths. After the coating step with the silane-containing solution, the silane-containing coating is firstly rinsed briefly once with demineralized water, without more substantial drying. The coated sheets are then dried at 120° C. in an oven for 5 minutes. Because of the interference colours, only the coatings on steel can be significantly examined visually, allowing an assessment of the homogeneity of the coating. The coatings without any complex fluoride content are very inhomogeneous. Surprisingly, a coating with titanium complex fluoride and zirconium complex fluoride proved to be markedly more homogeneous than when only one of these complex fluorides had been applied. An addition of nitroguanidine, nitrate or nitrite likewise improves the homogeneity of the coating. In some cases the layer thickness increases with the concentration of these substances.

(8) TABLE-US-00001 TABLE 1 Bath compositions in g/l, based on solids contents or, in the case of silanes, on the weight of the hydrolysed silanes; residual content: water and usually a very small amount of ethanol; process data and properties of the coatings Example/CE CE 1 CE 2 CE 3 CE 4 CE 5 CE 6 CE 7 CE 8 CE 9 CE 10 CE 11 E 1 CE 12 E 2 E 3 E 4 E 5 Organofunct. silane A 0.2 — 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Non-funct. silane C — 0.2 — — — — — — — 0.2 — — — — — — 0.1 H.sub.2TiF.sub.6 as Ti — — 0.2 — — 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 H.sub.2ZrF.sub.6 as Zr — — — 0.2 — 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Mn — — — — 0.3 — 0.1 0.3 0.5 0.5 — 0.3 0.2 0.2 0.2 0.2 0.2 H.sub.2O.sub.2 — — — — — — — — — — 0.03 0.03 — — — — — Nitrite — — — — — — — — — — — — — — 0.06 0.06 0.06 Nitrate — — — — — — — — — — — — 0.5 0.5 — 0.5 0.5 Na.sub.3PO.sub.4 as PO.sub.4 — — — — — — — — — — — — — 2 — — — Acetic acid — 0.02 — — 0.35 — — — — 0.02 — — — — — — 0.01 pH 10.5 5 4 4 4.5 4 4 4 4 4 4 4 4 4 4 4 4 BMW cross- cut test: score Steel 4 3 5 3 2-3 2 2 1 1 3 1 0 1 0 0 0 0 E-zinc on steel 3 4 4 4 3 1-2 2 1 1 2 1 0 1 0 0 0 0 Hot-dip zinc on steel 2 5 4 4 2 1 1 0 0 0 1 0 1 1 0 0 0 Al 6016 2 3 2 2 3 1 1 1 1 0 1 1 1 0 0 0 0 Galvaneal ® 1 2 1 2 1-2 1 1 1 0 0 1 0 1 0 0 0 0 10 VDA cycles, mm disbonding Steel 8 7 7 4 7 3 2 2 1.5 1.5 2 1.5 2 1 2 1.5 1.5 E-zinc on steel 5 5 3 4 5 2 1 1 1 1.5 1.5 1 1.5 0.5 1 1 1 Hot-dip zinc on steel 4 5 2.5 3.5 4 <1 1 <1 <1 <1 1.5 <1 1 <1 <1 <1 <1 Galvaneal ® 2 3 2 1.5 3 <1 <1 <1 <1 <1 1 <1 1 <1 1 1 0 Stone chip resistance after VDA stress: score Steel 5 5 4 4 5 2-3 2 1 1 1 2-3 2 2 1 2-3 2 1-2 E-zinc on steel 5 5 3 4 4 2 1-2 1 1 2 2-3 2 1-2 1 1-2 1-2 1 Hot-dip zinc on steel 5 5 3 4 4 1 1 1 0-1 1 1-2 1 1-2 1 1 1 1 Galvaneal ® 4 4 2 3 4 1-2 1 1 1 2 1-2 1 1-2 1 1 1 1 Salt spray test, 1008 h Steel 7 8 4 3.5 7 2 2 1.5 1 2.5 2.5 2 2.5 1.5 2 1.5 1.5 CASS test, mm disbonding Al 6016 6 5 3.5 3.5 6 2.5 2 1.5 1.5 1 2.5 2 2.5 2 2 2 2 Example/CE E 6 E 7 CE 13 CE 14 E 8 E 9 E 10 E 11 E 12 E 13 CE 15 E 14 CE 16 E 15 E 16 Organofunct. silane A 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.1 — 0.2 0.2 0.2 0.2 0.2 Organofunct. silane B — — — — — — — — 0.2 0.2 — — — — — H.sub.2TiF.sub.6 as Ti 0.2 0.2 — 0.2 0.2 0.2 0.2 0.2 0.2 0.2 — 0.2 0.2 0.2 — H.sub.2ZrF.sub.6 as Zr 0.2 0.2 — 0.2 0.2 0.4 0.4 0.2 0.2 0.2 — 0.2 0.2 0.2 — TiZr carbonate — — — — — — — — — — — — — — 0.4 Mn 0.3 0.3 — — 0.3 0.2 0.2 0.3 0.3 0.3 — 0.3 — 0.3 0.3 Nitrite 0.06 0.06 — — — — — — — — — — — — — Nitrate — 0.5 — — — — 1 — — — — — — — — Nitroguanidine — — 0.2 0.2 0.2 0.3 0.3 0.2 0.2 0.2 — — — — — Aminoguanidine — — — — — — — — — — 0.2 0.2 — — — Na.sub.3PO.sub.4 as PO.sub.4 — — — — — — — 2 — — — — — — — Phosphonate — — — — — — — — — — 0.05 0.05 0.05 Acetic acid — — 0.3 — — — — — — — — — — — 0.8 pH 4 4 7 4 4 4 4 4 4 4 11 4 4 4 7 BMW cross- cut test score Steel 1 0-1 2 1 1 0 0 1 0-1 0-1 2 1 2 2 1 E-zinc on steel 1 1 1 2 1 1 0 1 1 1 1 1 1-2 1 0-1 Hot-dip zinc on steel 0 0 2 0 0 0 0 0 0 0 2 0 1-2 1 1 Al 6016 1 1 2 1 1 1 0 1 1 1 2 1 2 1 0-1 Galvaneal ® 1 1 1 1 1 0 0 1 1 1 1 1 1 1 0-1 10 VDA cycles, mm disbonding Steel 2 1.5 8 2.5 2.5 2 1.5 2 1.5 1.5 8 2.5 2.5 2 5 E-zinc on steel 1 1 5 1.5 1.8 1.5 1 1 1 1 5 1 2 1.5 3 Hot-dip zinc on steel 1 1 4 <1 1 <1 <1 <1 1 1 4 <1 1 <1 2 Galvaneal ® <1 <1 2 <1 <1 <1 <1 <1 <1 <1 2 <1 1 1 1 Stone chip resistance after VDA stress: score Steel 1 0-1 5 2 1-2 1 1 1 0-1 0-1 5 1 3 1-2 3 E-zinc on steel 1 1 5 1-2 1-2 1-2 1 1 1 1 5 1 2 1 3 Hot- dip zinc on steel 1 1 5 1 1 1 1 1 1 1 5 1 2 1 2 Galvaneal ® 1 1 4 1 1 1 0 1 1 1 4 1 1 1 2 Salt spray test, 1008 h Steel 1.5 1 7 2.5 2 1 1 1.5 1 1 7 1.5 2.5 1.8 4 CASS test, mm disbonding Al 6016 1.5 1.5 6 3 1.5 1.5 1 1.5 1.5 1.5 6 1.5 2 1 3 Example/CE E 17 E 18 CE 17 CE 18 E 19 E 20 E 21 E 22 E 23 CE 19 Organofunct. 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 — silane A H.sub.2TiF.sub.6 as Ti — — — — — — 0.2 — 0.2 0.2 H.sub.2ZrF.sub.6 as Zr — — — — — 0.2 — 0.2 — — H.sub.3AlF.sub.6 as Al 0.2 — — 0.2 0.2 0.2 0.2 — — — H.sub.2BF.sub.4 as B — 0.2 — 0.2 0.2 — — 0.2 0.2 — H.sub.2SiF.sub.6 as Si — — 0.2 — — — — — — — Mn 0.3 0.3 0.3 — 0.3 0.3 0.3 0.3 0.3 — Nitrate — — — — — — — — — — Nitroguanidine 0.2 0.2 0.2 — 0.2 0.2 0.2 0.2 0.2 — pH 4 4 4 4 4 4 4 4 4 11

(9) Over the short period of use, all the bath compositions are found to be stable and satisfactory to apply. There are no precipitations and no colour changes, except in the case of compositions containing peroxide and titanium complex fluoride. There are no differences in behaviour, visual impression or test results between the different Examples and Comparative Examples which can be attributed to the treatment conditions, e.g. application by spraying, dipping or rollcoater treatment. The films formed are transparent and almost all are extensively homogeneous. They do not colour the coating. The structure, gloss and colour of the metallic surface appear to be only slightly changed by the coating. If a titanium and/or zirconium complex fluoride is present, iridescent layers are formed, especially on steel surfaces. Combining several silanes has not so far brought about a significant improvement in the corrosion protection, but this cannot be ruled out. Furthermore, a content of H.sub.3AlF.sub.6 was found on aluminium-rich metallic surfaces due to corresponding reactions in the aqueous composition. Surprisingly, however, combining two or three complex fluorides in the aqueous composition has proved extremely beneficial.

(10) The layer thickness of the coatings produced in this way—also dependent on the type of application, which was initially varied in specific experiments—ranged from 0.01 to 0.16 μm and usually from 0.02 to 0.12 μm and was often up to 0.08 μm, being markedly greater when organic polymer was added.

(11) The corrosion protection scores in the cross-cut test according to DIN EN ISO 2409, after storage for 40 hours in 5% NaCl solution according to BMW specification GS 90011, range from 0 to 5, 0 representing the best values. In the salt spray/condensation water alternation test over 10 cycles according to VDA test sheet 621-415 with alternating corrosion stress between salt spray test, perspiration water test and drying interval, the disbonding is measured on one side from the scratch outwards and reported in mm, the disbonding ideally being as small as possible. In the stone chip resistance test according to DIN 55996-1, the coated metallic sheets are bombarded with scrap steel after the aforementioned VDA alternation test over 10 cycles: The damage picture is characterized by scores from 0 to 5, 0 representing the best results. In the salt spray test according to DIN 50021 SS, the coated sheets are exposed for up to 1008 hours to an atomized corrosive sodium chloride solution; the disbonding is then measured in mm from the scratch outwards, the scratch being made with a standard gouge down to the metallic surface, and the disbonding ideally being as small as possible. In the CASS test according to DIN 50021 CASS, the coated sheets made of an aluminium alloy are exposed for 504 hours to an atomized special corrosive atmosphere; the disbonding is then measured in mm from the scratch outwards and ideally is as small as possible.

(12) Given that the development of the zinc/manganese/nickel phosphatizing of car bodies has spanned several decades, the phosphate layers of this type produced today are of extremely high quality. Nevertheless, contrary to expectation, it was possible to achieve the same high-quality properties with silane-containing coatings by means of aqueous silane-containing compositions that have only been in use for a few years, even though a greater effort was required.

(13) Other experiments on car body elements have shown that the electrochemical conditions of the CDL bath may be very slightly adaptable to the different kind of coating, but otherwise that the outstanding properties obtained in laboratory experiments can be reproduced on car body elements.