Method for coating metal surfaces of substrates and objects coated according to said method

Abstract

The invention relates to a method for coating surfaces, to a corresponding coating, and to the use of the objects coated according to said method. According to the invention, the method has or consists of the following steps: I. providing a substrate with a cleaned surface, II. contacting and coating the surfaces with an aqueous composition in the form of a dispersion and/or suspension, VI. if necessary rinsing the organic coating, and VII. drying and/or baking the organic coating or VIII. if necessary drying the organic coating and carrying out a coating process using a similar or additional coating composition prior to a drying and/or baking process, wherein between step I and step II, the coating process is carried out using an aqueous composition in the form of a dispersion and/or suspension on the basis of a colloidal silicate sol, which incorporates multivalent metal cations, or a silane- or silicate-modified polymer and if necessary a rinsing process is carried out.

Claims

1. A method for coating metallic surfaces of substrates, comprising the steps of: I. supplying a substrate having a cleaned metallic surface, II. coating the cleaned metallic surface with an aqueous composition in the form of a dispersion, suspension or a combination thereof of film-forming polymers consisting of a mixture of at least one stabilized polymer dispersion with a solids content of 30 to 80 wt % with a gelling agent in an amount of 0.001 to 20.0 wt %, based on the total mass of the resulting mixture as well as with cations, forming a coating based on an ionogenic gel, III. optionally rinsing the coating, drying the coating, baking the coating or a combination thereof, and IV. optionally forming another coating having a similar or additional coating composition before drying, baking, or a combination thereof, wherein between step I and step II, a coating is applied with an aqueous composition in the form of a dispersion, suspension, or a combination thereof based on a colloidal silicatic sol incorporating polyvalent metal cations and optionally a rinsing operation, wherein the polyvalent metal cations, when the aqueous composition includes a demineralized water, are added before the following other constituents: 0.725 g/L to 1.45 g/L of zinc nitrate and 0.22 g/L to 0.55 g/L of hexafluorozirconic acid and 0.66 g/L to 1.1 g/L of manganese nitrate adjusted to about pH 4.5 with sodium carbonate and 25 g/L of amorphous silica.

2. The method according to claim 1, characterized in that the gelling agent comprises: a) at least one polysaccharide based on glycogens, amyloses, amylopectins, calloses, agar, algins, alginates, pectins, carrageenan, celluloses, chitins, chitosans, curdlans, dextrans, fructans, collagens, gellan gum, gum arabic, starches, xanthans, gum tragacanth, karayans, tara gum or glucomannans; b) at least one anionic polyelectrolyte of natural origin, based on polyamino acids, collagens, polypeptides, or lignins; c) at least one synthetic anionic polyelectrolyte, based on polyamino acids, polyacrylic acids, polyacrylic acid copolymers, acrylamide copolymers, lignins, polyvinyl sulfonic acid, polycarboxylic acids, polyphosphoric acids or polystyrenes or combinations of a), b) or c).

3. The method according to claim 1, characterized in that the gelling agent comprises at least one polysaccharide, based on pectins, gellan gum or a combination thereof.

4. The method according to claim 1, characterized in that the aqueous composition, the coating or a combination thereof contain(s) a mixture of at least two different gelling agents.

5. The method according to claim 4, characterized in that the aqueous composition, the coating or a combination thereof contain(s) a mixture of two pectins.

6. The method according to claim 1, characterized in that the aqueous composition, the coating or a combination thereof contains 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 groups and carboxyl groups.

7. The method according to claim 1, characterized in that the aqueous composition, the coating or a combination thereof contains at least one anionic polysaccharide, at least one anionic polyelectrolyte or a combination thereof, selected from those with a molecular weight in the range of 500 to 1,000,000 g/mol.

8. The method according to claim 1, characterized in that the aqueous composition, the coating or a combination thereof contains at least one anionic polysaccharide, at least one anionic polyelectrolyte or a combination thereof, selected from those with a degree of amidation of the carboxyl functions in the range of 1 to 50% or a degree of epoxidation of the carboxyl functions of up to 80%.

9. The method according to claim 1, characterized in that the anionic polyelectrolytes are or have been modified with adhesion-promoting adhesive 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 having 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, siloxanes or combination thereof produced from the former, 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 the acetylacetones and ?-diketo groups, carbonyl groups and hydroxyl groups.

10. The method according to claim 1, characterized in that the aqueous composition, the coating or a combination thereof contains at least one complexing agent for metal cations or a polymer modified for complexing metal cations.

11. The method according to claim 10, characterized in that the aqueous composition, the coating or a combination thereof contains at least one complexing 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.

12. The method according to claim 1, characterized in that the aqueous composition, the coating or a combination thereof contains at least one type of cations, 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 Ag, Al, B, Ba, Ca, Co, Cu, Fe, In, Mg, Mn, Mo, Ni, Pb, Sn, Ta, Ti, V, W, Zn, Zr or combinations thereof.

13. The method according to claim 12, characterized in that Ag, Al, Cu, Fe, Mg, Zn or combinations thereof are selected as cations that have been dissolved out of the metallic surface, added to the aqueous composition for incorporation into the silicate-modified polymer or a combination thereof.

14. The method according to claim 1, characterized in that the aqueous composition contains a crosslinking agent selected from the group consisting of: silanes, siloxanes, phenolic resin types or amines in an amount of 0.01 g/L to 50 g/L.

15. The method according to claim 1, characterized in that the aqueous composition contains complex titanium, zirconium fluorides or a combination thereof in an amount of 0.01 g/L to 50 g/L.

16. The method according to claim 15, characterized in that the aqueous composition contains complex titanium, zirconium fluorides or a combination thereof in an amount of 0.01 g/L to 30 g/L.

17. The method according to claim 1, characterized in that the aqueous composition contains an amount of at least one defoaming agent.

18. The method according to claim 1, characterized in that the aqueous composition contains at least one additive selected from the group, consisting of: pigments, biocides, dispersion aids, film-forming aids, acidic additives for adjusting the pH, basic additives for adjusting the pH, thickeners, flow control agents and combinations thereof.

19. The method according to claim 1, characterized in that the metallic surfaces are cleaned, pickled, pretreated or a combination thereof before contacting and coating the metallic surfaces with an aqueous composition in process step II.

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

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

Description

EXAMPLES

(1) I. Substrates:

(2) 1. Cold-rolled, pass-through annealed steel without any other alloy ingredients according to DIN EN 10130 and with a sheet metal thickness of approximately 0.7-0.8 mm. 2. Electrolytically galvanized steel according to DIN EN 10153 and having a zinc layer of 75 g/m.sup.2 and a sheet metal thickness of approximately 0.7-0.8 mm. 3. Aluminum as an AlMgSi alloy according to the standard AA 6014 and having a sheet metal thickness of approximately 1.2 mm. 4. Rod of beech wood
II. Cleaning:

(3) The substrates are cleaned with an alkaline standard cleaner from the company Chemetall consisting of 30 g/L Gardoclean? S5176 and 4 g/L Gardobond? Additive H 7406 in tap water. The pH is adjusted to 10.5-10.8 with Gardobond? Additive H7143. The cleaning is done by spraying for 3 minutes at 60? C. and 0.6 bar. Next the sheet metal plates are rinsed thoroughly by dipping them in tapwater and deionized water.

(4) III. Silicate Coating:

(5) To produce the silicate-based pretreatment, 2.9 g/L Gardobond? Additive H7107 and 22 g/L Gardobond? Oxsilan? Additive 9906 from the company Chemetall are added to deionized water as the starting solution. Then the pH is adjusted to 4.5 with Gardobond? Oxsilan? Additive 9951, and 125 g/L Snowtex? O from the company Nissan Chemical is added. At the end, the mixture is topped off with deionized water and the bath is adjusted to a pH of 4.0 with dilute nitric acid.

(6) To incorporate polyvalent cations into the silicate coating during preparation, they must be added to the starting mix of deionized water before the other ingredients (see above).

(7) The substrates are treated in the immersion bath at 40? C. for the period of time specified in the examples and subsequently rinsed thoroughly for 2 minutes at room temperature in deionized water unless a different period of time is specified. In addition, the coatings produced in this form can optionally be dried before the following treatment without any loss of reactivity for the following coating step.

(8) IV. Deposition of Organic Formulation:

(9) The treated substrates are [treated] at room temperature for the period of time specified in the examples in an organic formulation based on ionogenic gelation according to the specification WO002013117611A1; the full content of this patent specification is herewith included, to check whether the metal cations in the silicate coating are sufficient to deposit the coating. Next the coated substrates are rinsed thoroughly in deionized water. The coating is dried in a circulating air oven for 5 minutes at 170? C. The resulting thickness of the overall coating is evaluated gravimetrically or by means of an eddy current measurement.

(10) V. X-Ray Fluorescence Analysis:

(11) To characterize the silicate coating, x-ray fluorescence analysis is used. The silicon and zirconium contents provide information about the layer thickness while calcium, magnesium or zinc provide information about the amount of cations incorporated into the layer.

(12) General Description of Experiments:

(13) Substrates 1 through 3 were pretreated with an alkaline spray cleaner according to point II, then subjected to a silicate-based pretreatment according to point III and then coated with the organic formulation described according to point IV.

Comparative Example 1

(14) Substrate 1 was coated with the organic formulation defined according to point IV by immersion for 5 minutes in the immersion bath without a silicate coating or metal ion incorporation according to point III. A dry film thickness of 20 ?m was determined by using an eddy current measuring instrument.

Comparative Example 2

(15) Substrate 2 was coated with the organic formulation defined according to point IV by immersion for 5 minutes in the immersion bath without a silicate coating or incorporation of metal ions according to point III. A dry film thickness of 41 ?m was determined by using an eddy current measuring instrument.

Comparative Example 3

(16) Substrate 3 was coated with the organic formulation defined according to point IV by immersion for 5 minutes in the immersion bath without a silicate coating or incorporation of metal ions according to point III. No dry film thickness was measured using an eddy current measuring instrument.

Comparative Example 4

(17) Substrate 3 was subjected to a silicate-based pretreatment according to point III for 5 minutes without the addition of metal salts and then coated with the organic formulation defined according to point IV for 5 minutes. No dry film thickness could be measured with an eddy current measuring instrument; an amount of 622 mg/m.sup.2 silicon and 55 mg/m.sup.2 zirconium was determined by x-ray fluorescence analysis according to point V.

Example 1

(18) Substrate 1 was subjected to a silicate-based pretreatment according to point III, with the addition of 24 g/L calcium nitrate tetrahydrate for five minutes and then coated with the organic formulation specified according to point IV for five minutes. A dry film thickness of 22 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 945 mg/m.sup.2 silicon, 10 mg/m.sup.2 zirconium and 5 mg/m.sup.2 calcium by means of x-ray fluorescence analysis according to point V.

Example 2

(19) Example 1 was repeated with substrate 2, and a dry film thickness of 44 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 1005 mg/m.sup.2 silicon, 12 mg/m.sup.2 zirconium and 9 mg/m.sup.2 calcium by means of x-ray fluorescence analysis according to point V.

Example 3

(20) Example 1 was repeated with substrate 3, and a dry film thickness of 11 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 1245 mg/m.sup.2 silicon, 12 mg/m.sup.2 zirconium and 10 mg/m.sup.2 calcium by means of x-ray fluorescence analysis according to point V.

Example 4

(21) Substrate 3 was subjected to a silicate-based pretreatment according to point III, with the addition of 47 g/L calcium nitrate tetrahydrate for five minutes, and then coated with the organic formulation described according to point IV for five minutes. A dry film thickness of 10 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 1505 mg/m.sup.2 silicon, 12 mg/m.sup.2 zirconium and 5 mg/m.sup.2 calcium by means of x-ray fluorescence analysis according to point V.

Example 5

(22) Example 4 was repeated, except that 71 g/L calcium nitrate tetrahydrate was used and a dry film thickness of 9 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 965 mg/m.sup.2 silicon, 8 mg/m.sup.2 zirconium and 5 mg/m.sup.2 calcium by means of x-ray fluorescence analysis according to point V.

Example 6

(23) Example 4 was repeated, except that 95 g/L calcium nitrate tetrahydrate was used and a dry film thickness of 2 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 116 mg/m.sup.2 silicon, 2 mg/m.sup.2 zirconium and <5 mg/m.sup.2 calcium by means of x-ray fluorescence analysis according to point V.

Example 7

(24) Substrate 3 was subjected to a silicate-based pretreatment according to point III, with the addition of 26 g/L magnesium nitrate hexahydrate for five minutes, and then coated with the organic formulation described according to point IV for five minutes. A dry film thickness of 3 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 800 mg/m.sup.2 silicon, 60 mg/m.sup.2 zirconium and 25 mg/m.sup.2 magnesium by means of x-ray fluorescence analysis according to point V.

Example 8

(25) Example 7 was repeated, except that 103 g/L magnesium nitrate hexahydrate was used and a dry film thickness of 5 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 1245 mg/m.sup.2 silicon, 18 mg/m.sup.2 zirconium and 15 mg/m.sup.2 magnesium by means of x-ray fluorescence analysis according to point V.

Example 9

(26) Substrate 3 was subjected to a silicate-based pretreatment according to point III, with the addition of 47 g/L zinc nitrate for five minutes, and then coated with the organic formulation described according to point IV for five minutes. A dry film thickness of 2 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 565 mg/m.sup.2 silicon, 82 mg/m.sup.2 zirconium and 25 mg/m.sup.2 zinc by means of x-ray fluorescence analysis according to point V.

Example 10

(27) Example 9 was repeated, except that 189 g/L zinc nitrate was used, and a dry film thickness of 8 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 1210 mg/m.sup.2 silicon, 78 mg/m.sup.2 zirconium and 50 mg/m.sup.2 zinc by means of x-ray fluorescence analysis according to point V.

Example 11

(28) Example 9 was repeated, except that 379 g/L zinc nitrate was used, and a dry film thickness of 0 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 63 mg/m.sup.2 silicon, 2 mg/m.sup.2 zirconium and 25 mg/m.sup.2 zinc by means of x-ray fluorescence analysis according to point V.

Example 12

(29) Substrate 3 was subjected to a silicate-based pretreatment according to point III, with the addition of 24 g/L calcium nitrate tetrahydrate for one minute, and then coated with the organic formulation described according to point IV for five minutes. A dry film thickness of 4 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 96 mg/m.sup.2 silicon, 2 mg/m.sup.2 zirconium and <5 mg/m.sup.2 calcium by means of x-ray fluorescence analysis according to point V.

Example 13

(30) Example 12 was repeated, except that the treatment time with calcium nitrate tetrahydrate was two minutes long. A dry film thickness of 5 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 300 mg/m.sup.2 silicon, 3 mg/m.sup.2 zirconium and <5 mg/m.sup.2 calcium, determined by means of x-ray fluorescence analysis according to point V.

Example 14

(31) Example 12 was repeated, except that the treatment time with calcium nitrate tetrahydrate was three minutes long. A dry film thickness of 13 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 665 mg/m.sup.2 silicon, 6 mg/m.sup.2 zirconium and <5 mg/m.sup.2 calcium, determined by means of x-ray fluorescence analysis according to point V.

Example 15

(32) Example 12 was repeated, except that the treatment time with calcium nitrate tetrahydrate was four minutes long. A dry film thickness of 15 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 1000 mg/m.sup.2 silicon, 8 mg/m.sup.2 zirconium and 5 mg/m.sup.2 calcium, determined by means of x-ray fluorescence analysis according to point V.

Example 16

(33) Example 12 was repeated, except that the treatment time with calcium nitrate tetrahydrate was ten minutes long. A dry film thickness of 20 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 1690 mg/m.sup.2 silicon, 13 mg/m.sup.2 zirconium and 10 mg/m.sup.2 calcium, determined by means of x-ray fluorescence analysis according to point V.

Example 17

(34) Example 12 was repeated, except that the treatment time with calcium nitrate tetrahydrate was five minutes long and then it was rinsed with deionized water for 60 minutes. A dry film thickness of 15 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 1470 mg/m.sup.2 silicon, 15 mg/m.sup.2 zirconium and <5 mg/m.sup.2 calcium, determined by means of x-ray fluorescence analysis according to point V.

Example 18

(35) Example 3 was repeated, except that the treatment time for the coating with the organic formulation described in point IV was 10 minutes long. A dry film thickness of 19 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 1245 mg/m.sup.2 silicon, 12 mg/m.sup.2 zirconium and 10 mg/m.sup.2 calcium, determined by means of x-ray fluorescence analysis according to point V.

Example 19

(36) Example 18 was repeated, except that the treatment time for the coating with the organic formulation described in point IV was 15 minutes long. A dry film thickness of 19 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 1245 mg/m.sup.2 silicon, 12 mg/m.sup.2 zirconium and 10 mg/m.sup.2 calcium, determined by means of x-ray fluorescence analysis according to point V.

Example 20

(37) Example 18 was repeated, except that the treatment time for the coating with the organic formulation described in point IV was 20 minutes long. A dry film thickness of 19 ?m was measured using an eddy current measuring instrument, and the weight per unit of area was found to be 1245 mg/m.sup.2 silicon, 12 mg/m.sup.2 zirconium and 10 mg/m.sup.2 calcium, determined by means of x-ray fluorescence analysis according to point V.

Example 21

(38) Example 1 was repeated and a dry film thickness of 50 ?m was determined gravimetrically.

(39) All the micrographs show a homogenous layer was formed, indicating that this is a reliable, self-regulating and readily controllable coating method.