Method for Coating Metal Surfaces of Substrates and Objects Coated in Accordance With Said Method

Abstract

The invention relates to a method for coating surfaces, to a corresponding coating, and to the use of the objects coated in accordance with said method. In accordance with the invention the object is achieved by a method for coating metallic surfaces of substrates that comprises or consists of the following steps: I) providing a substrate having a cleaned metallic surface, II) contacting and coating metallic surfaces with an aqueous composition in dispersion and/or suspension form, III) optionally rinsing the organic coating, and IV) drying and/or baking the organic coating or V) optionally drying the organic coating and coating it with a similar or further coating composition prior to drying and/or baking, characterized in that the coating in step II is carried out with an aqueous composition in dispersion and/or suspension form that comprises a complex fluoride, and at least one anionic polyelectrolyte is added to a nonionically or anionically/nonionically stabilized dispersion of film-forming polymers and/or to a suspension of film-forming inorganic particles and a coating forms that is based on an ionogenic gel comprising cations dissolved out of the metallic surface.

Claims

1. A method comprising: I. Providing a substrate with a purified metal surface, II. Contacting and coating the metal surface with an aqueous composition in the form of a dispersion and/or suspension to form an organic coating, III. Optionally rinsing the organic coating, and IV. Drying and/or baking the organic coating, or V. Optionally drying the organic coating and applying a similar or additional coating composition as an additional coating prior to drying and/or baking, characterized in that, in step II, the aqueous composition comprises a complex fluoride, selected from the group consisting of hexa- or tetrafluorides of the elements titanium, zirconium, hafnium, silicon, aluminum and/or boron in an amount in the range of 1.1.10.sup.6 mol/liter to 0.30 mol/liter, based on the cations, wherein at least one nonionic or anionic-nonionic polyelectrolyte is added in an amount in the range of 0.01 to 5.0% by weight, based on the total weight of the resulting mixture, is added to the nonionically or anionically-nonionically stabilized dispersion of film-forming polymers and/or a suspension of film-forming inorganic particles with a solids content in the range of 2 to 40% by weight and an average particle size in the range of 10 to 1000 nm, which is stable in a pH range of 0.5 to 7.0, wherein the aqueous composition has a pH in the range of 0.5 to 7.0 and forms a coating based on an ionogenic gel which binds cations dissolved out of the metallic surface and these cations originate from a pretreatment step and/or from the contacting in step II.

2. The method according to claim 1, characterized in that a complex fluoride is present in an amount in the range of 1.1.10.sup.5 mol/liter to 0.15 mol/liter based on the cations, wherein the aqueous composition has a pH in the range of 1.0 to 6.0.

3. The method according to claim 1, characterized in that at least one anionic polyelectrolyte is selected from the groups a) polysaccharides, based on glycogens, amyloses, amylopectins, calloses, agar, algines, alginates, pectins, carrageenans, celluloses, chitins, chitosans, curdlans, dextrans, fructans, collagens, gellan gum, gum arabic, starches, xanthans, gum tragacanth, karayans, tara gum and glucomannans; b) anionic polyelectrolytes of natural origin, based on polyamino acids, collagens, polypeptides, lignins and/or c) synthetic anionic polyelectrolytes, based on polyamino acids, polyacrylic acids, polyacrylic acid copolymers, acrylamide copolymers, lignins, polyvinyl sulfonic acid, polycarboxylic acids, polyphosphoric acids or polystyrenes.

4. The method according to claim 1, characterized in that the anionic polyelectrolyte comprises at least one polysaccharide, based on pectins or gellan gum.

5. The method according to claim 1, characterized in that the aqueous composition and/or the organic coating produced therefrom comprises a mixture of at least two different nonionic or anionic-nonionic polyelectrolytes.

6. The method according to claim 5, characterized in that the aqueous composition and/or the organic coating produced therefrom contain(s) a mixture of two pectins.

7. The method according to claim 1, characterized in that the aqueous composition and/or the organic coating produced therefrom comprises at least one anionic polysaccharide selected from those with a degree of esterification of the carboxyl function in the range of 5 to 75% based on the total number of alcohol and carboxyl groups.

8. The method according to claim 1, characterized in that the aqueous composition and/or the organic coating produced therefrom comprises at least one polysaccharide and/or at least one additional polyelectrolyte selected from those with a molecular weight in the range of 500 to 1,000,000 g/mol.sup.1.

9. The method according to claim 1, characterized in that the aqueous composition and/or the organic coating produced therefrom contain(s) at least one polysaccharide and/or at least one additional polyelectrolyte selected from those with a degree of amidation of the carboxyl functions in the range of 1 to 50%, a degree of epoxidation of the carboxyl functions of up to 80%.

10. The method according to claim 1, characterized in that the polyelectrolytes are modified with adhesion-promoting adhesion groups selected from the group consisting of chemical groups of multifunctional epoxies, isocyanates, primary amines, secondary amines, tertiary amines, quaternary amines, amides, imides, imidazoles, formamides, Michael reaction products, carbodiimides, carbenes, cyclic carbenes, cyclocarbonates, multifunctional carboxylic acids, amino acids, nucleic acids, methacrylamides, polyacrylic acids, polyacrylic acid derivatives, polyvinyl alcohols, polyphenols, polyols with at least one alkyl and/or aryl radical, caprolactam, phosphoric acids, phosphoric acid esters, epoxy esters, sulfonic acids, sulfonic acid esters, vinyl sulfonic acids, vinyl phosphonic acids, catechol, silanes as well as the silanols and/or siloxanes formed therefrom, triazines, thiazoles, thiazines, dithiazines, acetals, hemiacetals, quinones, saturated fatty acids, unsaturated fatty acids, alkyds, esters, polyesters, ethers, glycols, cyclic ethers, crown ethers, anhydrides as well as acetyl acetones and beta-diketo groups, carbonyl groups and hydroxyl groups.

11. The method according to claim 1, characterized in that the aqueous composition and/or the organic coating produced therefrom comprises at least one chelating agent for metal cations or a polymer modified to be a chelating agent for metal cations.

12. The method according to claim 11, characterized in that the aqueous composition and/or the organic coating produced therefrom comprises at least one chelating agent selected from those based on maleic acid, alendronic acid, itaconic acid, citraconic acid or mesaconic acid or the anhydrides or hemiesters of these carboxylic acids.

13. The method according to claim 1, characterized in that the aqueous composition and/or the organic coating produced therefrom comprises at least one type of cation, selected from those based on cationic salts selected from the group consisting of melamine salts, nitroso salts, oxonium salts, ammonium salts, salts with quaternary nitrogen cations, salts of ammonium derivatives and metal salts of Al, B, Ba, Ca, Cr, Co, Cu, Fe, Hf, In, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Pb, Sn, Ta, Ti, V, W, Zn and/or Zr.

14. The method according to claim 13, characterized in that the cations that are dissolved out of the metallic surface or are added to the aqueous composition are selected from Al, Cu, Fe, Mg and/or Zn.

15. The method according to claim 1, characterized in that the aqueous composition and/or the organic coating produced therefrom comprises organic particles based on polyacrylates, polyurethanes, polyepoxides and/or their hybrids.

16. The method according to claim 1, characterized in that the aqueous composition and/or the organic coating produced therefrom comprises at least one emulsifier.

17. The method according to claim 16, characterized in that the aqueous composition and/or the organic coating produced therefrom comprises at least one emulsifier.

18. The method according to claim 1, characterized in that the aqueous composition and/or the organic coating produced therefrom comprises at least one additive selected from of the group consisting of biocides, dispersants, film-forming aids, acidic or basic aids for adjusting the pH, thickeners and flow control agents.

19. The method according to claim 1, characterized in that the aqueous composition forms the coating based on an ionogenic gel, and a dry film formed then or later has a thickness of at least 1 m.

20. The method according to claim 1, characterized in that the organic coating is formed in 0.05 to 20 minutes in a dip coating bath and after drying has a dry film thickness in the range of 5 to 100 m.

21. An aqueous composition comprising in an anionically stabilized dispersion of film-forming polymers and/or a suspension of film-forming inorganic particles with a solids content in the range of 2 to 40% by weight and an average particle size in the range of 10 to 1000 nm, which is stable in the pH range of 0.5 to 7.0, at least one polyelectrolyte in an amount in the range of 0.01 to 5.0% by weight, based on the total amount of the resulting mixture as well as a complex fluoride selected from the group consisting of hexafluorides or tetrafluorides of the elements titanium, zirconium, hafnium, silicon, aluminum and/or boron in an amount in the range of 1.1.10.sup.6 mol/liter to 0.30 mol/liter, based on the cations, wherein the aqueous composition has a pH in the range of 4 to 11.

22. The aqueous composition according to claim 21, characterized in that the dispersion of film-forming polymers comprises organic particles based on polyacrylates, polyurethanes, polyepoxies and/or their hybrids, further comprises at least one chelating agent, selected from those based on maleic acid, alendronic acid, itaconic acid, citraconic acid or mesaconic acid or anhydrides or hemiesters of these carboxylic acids and further comprises at least one anionic polyelectrolyte based on pectins or gellan gum.

23. The method according to claim 1, wherein the substrate was previously unsuccessfully coated by electro-dip coating.

Description

EXAMPLE 1

[0135] Substrate 1 was mixed with a mixture of 0.25% by weight, based on the total amount of the resulting mixture, with a pectin with a molecular weight of approx. 70,000 g/mol, a degree of amidation of 0%, a degree of esterification of 52%, a degree of epoxidation of 0%, a galacturonic acid content of 87% and 0.25% by weight, based on the total amount of the resulting mixture, and a pectin with a molecular weight of approx. 70,000 g/mol, a degree of amidation of 0%, a degree of esterification of 10%, a degree of epoxidation of 0%, a galacturonic acid content of 85% with 99.5% by weight of dispersion C described above was mixed with a mixture of 0.25% by weight. Then 10.0 g/L 20% hexafluorozirconic acid was added to this mixture. A dry film with a thickness of 20 m to 25 m was measured using an eddy current meter and SEM.

EXAMPLE 2

[0136] Experiment 1 was repeated using substrate 2 and a dry film thickness of 20 m to 25 m was found by SEM.

EXAMPLE 3

[0137] Experiment 1 was repeated with substrate 3 and a dry film thickness of 5 m to 10 m was determined by SEM.

EXAMPLE 4

[0138] Substrate 3 was mixed with a pectin having a molecular weight of approx. 70,000 g/mol, a degree of amidation of 0%, a degree of esterification of 52%, a degree of epoxidation of 0%, a galacturonic acid content of 87% and 0.25% by weight, based on the total amount of the resulting mixture, a pectin with a molecular weight of approx. 70,000 g/mol, a degree of amidation of 0%, a degree of esterification of 10%, a degree of epoxidation of 0%, a galacturonic acid content of 85% with 99.5% by weight of dispersion C, mixed with a mixture of 0.25% by weight, based on the total amount of the resulting mixture. Then 10.0 g/liter 20% hexafluorotitanic acid was added to the mixture. A dry film thickness of 8 m to 10 m was measured using an eddy current meter and SEM.

COMPARATIVE EXAMPLE 1

[0139] Substrate 1 was coated with dispersion A. No dry film thickness was determined by SEM.

COMPARATIVE EXAMPLE 2

[0140] Substrate 2 was coated with dispersion A. No dry film thickness was determined by SEM.

COMPARATIVE EXAMPLE 3

[0141] Substrate 3 was coated with dispersion A. No dry film thickness was determined by SEM.

COMPARATIVE EXAMPLE 4

[0142] Coating of substrate 1 with the polyelectrolytes mentioned in the description of the invention without mixing with the dispersion A yielded a dry film thickness of 300 nm to 500 nm.

COMPARATIVE EXAMPLE 5

[0143] Coating of substrate 2 with the polyelectrolytes mentioned in the description of the invention without mixing it with dispersion A, yielded a dry film thickness of 300 nm to 500 nm.

Comparative Example 6

[0144] The coating of substrate 3 with the polyelectrolytes mentioned in the description of the invention without mixing it with dispersion A yielded a dry film thickness of 300 nm to 500 nm.

COMPARATIVE EXAMPLE 7

[0145] Substrate 3 was coated by immersion in a mixture of 0.25% by weight, based on the total amount of the resulting mixture with a pectin with a molecular weight of approx. 70,000 g/mol, a degree of amidation of 0%, a degree of esterification of 52%, a degree of epoxidation of 0%, a galacturonic acid content of 87% and 0.25% by weight, based on the total amount of the resulting mixture, a pectin with a molecular weight of approx. 70,000 g/mol, a degree of amidation of 0%, a degree of esterification of 10%, a degree of epoxidation of 0%, a galacturonic acid content of 85% with 99.5% by weight of dispersion A described above. No dry film thickness could be detected.

COMPARATIVE EXAMPLE 8

[0146] Substrate 1 was coated with a mixture of 0.25% by weight, based on the total amount of the resulting mixture with a pectin with a molecular weight of approx. 70,000 g/mol, a degree of amidation of 0%, a degree of esterification of 52%, a degree of epoxidation of 0%, a galacturonic acid content of 87% and 0.25% by weight, based on the total amount of the resulting mixture, a pectin with a molecular weight of approx. 70,000 g/mol, a degree of amidation of 0%, a degree of esterification of 10%, a degree of epoxidation of 0%, a galacturonic acid content of 85% with 99.5% by weight of the dispersion B described above. 2.0 g/L 20% hexafluorozirconic acid was added to this mixture, forming a dry film with a thickness of 55 m to 65 m, measured using an eddy current meter and SEM.

COMPARATIVE EXAMPLE 9

[0147] Comparative Example 8 was repeated with substrate 2 and a dry film thickness of 15 m to 25 m determined by SEM.

COMPARATIVE EXAMPLE 10

[0148] Comparative Example 8 was repeated with substrate 3 and a dry film thickness of 3 m to 4 m determined by SEM.

[0149] The micrographs all showed a homogenous layer formation, which indicates a reliable self-regulating and readily controllable coating method.