Aqueous agent and coating method for the anticorrosive treatment of metallic substrates

Abstract

An aqueous agent for the anticorrosive treatment of metallic substrates and to a method for coating such substrates. The aqueous agent according to this invention includes at least one compound that dissociates into zirconium- or titanium-fluorine complexes in aqueous solution, at least one water-soluble compound that releases metal cations, the metal cations being selected from the group composed of: iron-, copper-, or silver ions, and a water-soluble alkoxysilane that has at least one epoxy group.

Claims

1. An aqueous conversion solution for an anticorrosive treatment of metallic substrates as a pre-treatment for a further lacquer coating, including: at least one compound that dissociates into zirconium- or titanium-flourine complexes in aqueous solution, at least one water-soluble compound that releases metal cations, selected from the group composed of: iron-, copper-, or silver ions, and a water-soluble alkoxysilane that has at least one epoxy group as an adhesion-promoting phase, the alkoxysilane comprising a [3-2(2,3-epoxypropoxy)-propyl]-trimethoxysilane, a [3-2(2,3-epoxypropoxy)-propyl]-triethoxysilane, a [3-2(2, 3 -epoxypropoxy)-propyl]-methyldiethoxysilane, a [3-2(2,3 -epoxypropoxy)-propyl]-methyldimethoxysilane, a [3-2(2,3-epoxypropoxy)-propyl]-dimethylethoxysilane, or combinations thereof. wherein the conversion solution is essentially free of phosphate, chromium, and silanes having amino groups, and the epoxy group of the adhesion-promoting phase reacts with an amino group of the further lacquer coating.

2. The aqueous conversion solution according to claim 1, wherein the compound that dissociates into zirconium- or titanium-fluorine complexes in aqueous solution is selected from the group composed of: dipotassium hexafluorozirconate, disodium hexafluorozirconate, ammonium hexafluorozirconate, magnesium hexafluorozirconate, dilithium hexafluorozirconate and combinations thereof, as well as the analogous titanium-fluorine compounds and combinations thereof.

3. The aqueous conversion solution according to claim 2, wherein the concentration of zirconium lies in a range from 10.sup.?5 mol/l to 10.sup.?1 mol/l.

4. The aqueous conversion solution according to claim 3, wherein the compound that releases metal cations is selected from the group composed of: iron chlorides, iron citrates, iron sulfates, iron nitrates, iron acetates, iron tartrates, iron-carboxylic acid compounds, copper acetates, copper chlorides, copper nitrates, copper sulfates, copper-carboxylic acid compounds, silver chlorides, silver acetates, silver sulfates, silver nitrates, and combinations thereof.

5. The aqueous conversion solution according to claim 4, wherein the concentration of the metal cations lies in a range from 10.sup.?6 mol/l to 10.sup.?1 mol/l.

6. The aqueous conversion solution according to claim 5, wherein a proportion by weight of the alkoxysilane is between 0.45 wt. % and 5 wt.

7. The aqueous conversion solution according to claim 6, wherein a pH-Wert of the conversion solution lies in a range between 2.5 and 5.

8. The aqueous conversion solution according to claim 1, wherein the concentration of zirconium lies in a range 2*10.sup.?5 mol/l to 10.sup.?2 mol/l.

9. The aqueous conversion solution according to claim 1, wherein the compound that releases metal cations is selected from the group composed of: iron chlorides, iron citrates, iron sulfates, iron nitrates, iron acetates, iron tartrates, iron-carboxylic acid compounds, copper acetates, copper chlorides, copper nitrates, copper sulfates, copper-carboxylic acid compounds, silver chlorides, silver acetates, silver sulfates, silver nitrates, and combinations thereof.

10. A coating method, for an anticorrosive treatment, for metallic substrates, including the following method steps: producing the conversion solution of claim 1 by adding a water soluble compound that releases the metal cations, selected from the group composed of: iron-, copper-, or silver ions, in an aqueous solution that contains dissociated zirconium- or titanium-fluorine complexes, adjusting a pH value of the solution, through adding a buffer substance, to a pH value between 2.5 and 5, and adding the alkoxysilane to the solution, where the alkoxysilane has the at least one epoxy group; applying the conversion solution onto the substrate through immersion, spraying, or coating at room temperature and for a duration between 0.5 s and 500 s; and drying the treated substrate.

11. The method according to claim 10, wherein the drying is carried out in a flow of nitrogen or air, by sublimation drying, and/or through the use of IR-, NIR- or UV radiation.

12. The method according to claim 11, wherein the conversion solution is the aqueous agent according to claim 9.

13. The method according to claim 12, wherein after a method step of the drying, a forced drying takes place at 40? C. to 120? C.

14. The method according to claim 13, wherein before the method step of the application of the conversion solution, a cleaning of the substrate takes place.

15. The method according to claim 14, wherein the method also includes a coating of the treated substrate with a paint system.

16. The aqueous conversion solution according to claim 1, wherein the concentration of the metal cations lies in a range from 10.sup.?6 mol/l to 10.sup.?1 mol/l.

17. The aqueous conversion solution according to claim 1, wherein a proportion by weight of the alkoxysilane is between 0.45 wt. % and 5 wt. %.

18. The aqueous conversion solution according to claim 1, wherein a pH-Wert of the conversion solution lies in a range between 2.5 and 5.

19. The method according to claim 10, wherein the conversion solution is the aqueous agent according to claim 1.

20. The method according to claim 10, wherein after a method step of the drying, a forced drying takes place at 40? C. to 120? C.

21. The method according to claim 10, wherein before the method step of the application of the conversion solution, a cleaning of the substrate takes place.

22. The method according to claim 10, wherein the method also includes a coating of the treated substrate with a paint system.

23. The aqueous conversion solution according to claim 1, further comprising a buffer system for adjustment of a pH value.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) This invention is explained below in view of a schematic view of a treated substrate.

(2) FIG. 1 shows an exemplary embodiment of a schematic layer structure of a treated substrate according to this invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) In detail, FIG. 1 shows a cross-section through a part of a treated substrate. The illustration is only intended to clarify the basic layer structure of the treated substrate. It is not suitable for providing any information regarding layer thickness or layer transitions.

(4) The boundaries between the individual layers 1, 2, 3, 4 are shown as broken lines in order to clarify that there is generally not an abrupt transition between the layers 1, 2, 3, 4, but rather a smooth transition within a particular region.

(5) In the example shown in FIG. 1, the metallic substrate to be treated is represented in the form of a hot-dip galvanized sheet steel. The galvanized steel plate therefore includes a bottom layer 1, which is essentially composed of steel, and a zinc coating 2. The zinc coating 2 primarily contains zinc and zinc oxide. Instead of the layers 1 and 2, it is also possible to use other treated or untreated substrates such as aluminum alloys, ZnAlMg alloys, magnesium alloys, or the like.

(6) An overlying conversion layer 3 is produced through a conversion treatment of the substrate. To that end, the substrate is brought into contact with the conversion solution after being cleaned for several seconds in a bath system. By subsequent drying at 80? C. to 100? C., it is possible to achieve a good adhesion of the layers 2 and 3 through covalent bonding of silanes to the substrate surface 2. The alkoxysilanes contained in the conversion layer 3 provide a good adhesion of the corrosion protection coating 3 both to the zinc coating 2 and to the paint layer 4 that is applied as the top layer. Organic compounds contained in the paint layer 4 have amino groups so that a reaction of these amino groups with the epoxy groups of the silane can take place, which yields an improved bonding of the conversion layer 3 to the paint layer 4.