Anti-corrosion agent forming a coating film with good adhesion and method for nongalvanic application thereof
The invention relates to an aqueous coating material for metallic substrates, comprising a water-dispersible and/or water-soluble polymer P with a gradient in the concentration of covalently bonded hydrophilic groups along the main polymer chain, the polymer P having covalently bonded ligands A, which form chelates with the metal ions released during the corrosion of the substrate and/or with the substrate surface, and having crosslinking functional groups B, which with themselves, with further complementary functional groups B′ of the polymer P and/or with further functional groups B and/or B′ are able to form covalent bonds to crosslinkers V.
1. A two-stage process for the corrosion-control treatment of a metallic substrate, which comprises
(I) in a first stage immersing the substrate in a bath of an aqueous corrosion preventative K, which results in conversion at the substrate surface, and
(II) in a second stage immersing the substrate treated as per stage (I) in a bath of an aqueous coating material comprising, as a coating material, a water-dispersible and/or water-soluble polymer P with a gradient in the concentration of covalently bonded hydrophilic groups along the polymer main chain, the polymer P comprising covalently bonded ligands A, the ligands A being distributed randomly in the polymer P and being capable of forming chelates with metal ions released during the corrosion of the substrate and/or with a surface of the substrate, and crosslinking functional groups B, the crosslinking functional groups B being capable of forming covalent bonds to one or more crosslinkers V.
2. The process of claim 1 , wherein aqueous corrosion preventative K comprises
at least one compound having as its cation a lanthanide metal and/or a d-element metal bar chromium and/or as its anion a d-element metallate, with the exception of metallates containing chromium, and
at least one acid capable of oxidation, with the exception of phosphorus and/or chromium acids.
3. A process for the autophoretic application of an aqueous coating material to a metallic substrate, comprising depositing an aqueous coating material comprising, as a coating material, a water-dispersible and/or water-soluble polymer P with a gradient in the concentration of covalently bonded hydrophilic groups along the polymer main chain, the polymer P comprising covalently bonded ligands A, the ligands A being distributed randomly in the polymer P and being capable of forming chelates with metal ions released during the corrosion of the substrate and/or with a surface of the substrate, and crosslinking functional groups B, the crosslinking functional groups B being capable of forming covalent bonds to one or more crosslinkers V, wherein the thickness of the coating material on the substrate after autophoretic application is between 5 and 900 nm.
4. The process of claim 3 , wherein the hydrophilic groups comprise groups selected from ionic functional groups, primary amine, secondary amine, tertiary amine, amide groups, oligoalkoxy substituents, polyalkoxy substituents, etherified oligoalkoxy substituents, etherified polyalkoxy substituents and combinations thereof.
5. The process of claim 3 for the corrosion-control treatment of a metallic substrate, comprising
immersing a metallic substrate in a bath of the aqueous coating material, wherein the metallic substrate is immersed in the bath for a time of 1 second to 15 minutes and at a temperature between 20 and 90° C.
6. The process of claim 3 , wherein following the deposition of the coating material, the substrate is aftertreated thermally at temperatures between 50 and 200° C. and/or by irradiation.
7. The process of claim 3 , wherein the substrate contains at least 20% by weight of a metal selected from the group consisting of Fe, Al and/or Zn.
8. A process for the autophoretic application of an aqueous coating material to a metallic substrate, comprising depositing an aqueous coating material comprising, as a coating material, a water-dispersible and/or water-soluble polymer P with a gradient in the concentration of covalently bonded hydrophilic groups along the polymer main chain, the polymer P comprising covalently bonded ligands A which form chelates with metal ions released during the corrosion of the substrate and/or with a surface of the substrate, and crosslinking functional groups B, the crosslinking functional groups B being capable of forming covalent bonds to one or more crosslinkers V, wherein the thickness of the coating material on the substrate after autophoretic application is between 5 and 900 nm, further wherein the ligands A are distributed randomly in the polymer P.