Process for coating metallic surfaces of substrates and articles coated by this process

Abstract

A method for coating metallic surfaces of substrates with surfaces of aqueous (coating) compositions in the form of a dispersion and/or a suspension containing at least one stabilized binder and a gelling agent, the cations having been dissolved out of the metallic surface of the substrate in a pretreatment stage and/or during the contacting. The invention further relates to such a coating based on an ionogenic gel, in which the coating is formed by a process further described herein.

Claims

1. A process for coating metallic surfaces of substrates with aqueous organic compositions, the process comprising the steps of: I) providing a substrate with a cleaned metallic surface, II) contacting and coating the cleaned or pretreated metallic surface with a first aqueous organic composition in the form of a dispersion, suspension or combination thereof, the first aqueous organic composition comprising a first stabilized binder and a gelling agent, so as to form a first organic coating, III) optionally rinsing the first organic coating, IV) optionally drying the first organic coating, and V) coating the first organic coating with at least two additional aqueous organic compositions each comprising a stabilized binder and a gelling agent before drying and crosslinking all applied layers, wherein at least one of the at least two additional aqueous organic compositions comprises a stabilized binder that is different from the first stabilized binder and not present in the first aqueous organic composition or a gelling agent that is different from the first gelling agent and not present in the first aqueous organic composition, wherein the respective coating compositions each must fulfill the following conditions: a) be in the form of an aqueous mixture of deionized water, the gelling agent in an amount in the range of 0.2% to 2% by weight based on the weight of the coating composition and 5% to 20% by weight of the respective stabilized binder based on the weight of the coating composition; and b) be adjusted to a pH in the range of 1 to 7; and wherein c) a cleaned substrate is immersed in the aqueous mixture or at least 1 minute at room temperature, and d) a check is performed on whether an organic coating having a thickness of at least 1 μm has been deposited on the cleaned substrate, wherein each of the coatings forms a layer based on an ionogenic gel with cations that have been dissolved out of the metallic surface in the pretreatment stage and/or during the contacting, wherein the dry film thickness of all the deposited coatings after drying and crosslinking all of them is in the range of 3 to 500 μm, and wherein the aqueous compositions and the organic coatings produced from them contain at least one complexing agent from metal cations or a polymer which is modified so as to complex metal cations.

2. The process according to claim 1, wherein the amount of gelling agent in a) is in the range of 0.3% to 1%, the amount of stabilized binder in a) is in the range of 7% to 15%, the pH in b) is in the range of 1.5 to 5 and is adjusted through use of a mineral acid, the immersion in c) is conducted for at least in the range of 2 to 15 minutes at room temperature, and the average thickness in d) is at least 2 μm.

3. The process according to claim 1 characterized in that each of the stabilized binders is selected from the group consisting of nonionically stabilized polyepoxy dispersions, nonionically stabilized polyurethane dispersions and ionically stabilized polyacrylate dispersions.

4. The process according to claim 1, characterized in that each of the aqueous compositions contains a stabilized dispersion with a solids content in the range of 20% to 90% by weight based on the total mass of the resulting mixture and at least one gelling agent in an amount of 0.001% to 20.0% by weight, based on the total mass of the resulting mixture, each aqueous composition having a viscosity in the range of 100 to 5000 mPas, a density in the range of 1.0 to 1.2 g/cm.sup.3 and a pH in the range of 0.5 to 10.

5. The process according to claim 1, characterized in that each of the aqueous compositions additionally contains one or more of a) to d): a) 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, b) complex titanium and/or zirconium fluorides in an amount of 0.01 g/L to 50 g/L, c) an amount of at least one foam suppressant, and d) at least one additive selected from the group consisting of pigments, biocides, dispersant aids, film-forming aids, acidic and/or basic aids for adjusting the pH and thickeners and flow control agents.

6. The process according to claim 1, characterized in that the gelling agent is selected from the group consisting of 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, karaya gums, tara gums and glucomannans; b) at least one anionic polyelectrolyte of natural origin based on polyamino acids, collagens, polypeptides, lignins and 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.

7. The process according to claim 1, characterized in that the aqueous compositions and the organic coatings produced from them contain 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.

8. The process according to claim 1, characterized in that the aqueous compositions and the organic coatings produced from them contain at least one anionic polysaccharide and/or at least one anionic polyelectrolyte selected from those with a molecular weight in the range of 500 to 1,000,000 g/mol.sup.−1.

9. The process according to claim 1, characterized in that the aqueous compositions and the organic coatings produced from them contain at least one anionic polysaccharide or at least one anionic polyelectrolyte 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%.

10. The process according to claim 1, characterized in that the aqueous compositions and the organic coatings produced from them contain anionic polyelectrolytes that are modified with 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 with at least one alkyl group and/or aryl group, 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 produced therefrom and 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 β-diketo groups, carbonyl groups and hydroxyl groups.

11. The process according to claim 1, characterized in that the aqueous compositions and the organic coatings produced from them contain 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 process according to claim 1, characterized in that the aqueous compositions and the organic coatings produced from them contain at least one type of cations selected from those based on cationically active 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, Ba, Ca, Co, Cu, Fe, In, Mg, Mn, Mo, Ni, Pb, Sn, Ta, Ti, V, W, Zn and/or Zr.

13. The process according to claim 1, characterized in that the aqueous compositions contain complex titanium and/or zirconium fluorides in an amount in the range of 0.1 g/L to 30 g/L.

14. The process according to claim 1, characterized in that each of the aqueous compositions forms a coating based on an ionogenic gel, wherein the layer thickness of all the deposited coatings after drying and crosslinking of all the applied layers is in the range of 5 to 300 μm and 2 to 10 layers are deposited.

15. The process according to claim 1, characterized in that the individual organic coatings are formed in a time in the range of 0.05 to 20 minutes in the immersion bath and after drying they have a dry film thickness in the range of 1 to 100 μm.

16. The process according to claim 1, wherein each stabilized binder of the at least one of the at least two additional aqueous organic compositions is not present in the first aqueous organic composition.

17. The process according to claim 1, wherein each gelling agent of the at least one of the at least two additional aqueous organic compositions is not present in the first aqueous organic composition.

Description

EXAMPLES

(1) First a general description of the materials used and the procedure for carrying out the process:

(2) A. Substrates:

(3) Electrolytically galvanized steel plate with a zinc layer application of 5 μm, sheet metal thickness 0.81 mm, 2. Cold rolled steel, sheet metal thickness approximately 0.8 mm, 3. Aluminum alloy of the quality class AC 170, sheet metal thickness approximately 1.0 mm
B. Alkaline Cleaning: 1. 30 g/L Gardoclean® S 5176 and 4 g/L Gardobond® additive H 7406 from Chemetall GmbH prepared in tap water. The sheet metal plates were cleaned for 180 s in a spray bath at 60° C. and then rinsed for 120 s with tap water and 120 s with deionized water in an immersion bath.
C. Pretreatment: Pretreatment based on zinc phosphate (Gardobond 26S from Chemetall GmbH) 2. Pretreatment based on silane (Oxsilan 9810/2 from Chemetall GmbH)

(4) Coating the surfaces with formulations according to the invention for forming the organic coating:

(5) All mixtures were applied to the respective substrate by means of immersion bath at room temperature within 5 minutes.

(6) D. Ingredients of the Formulation:

(7) All data in the following table refers to the percentage amount by weight in the as-delivered form of the respective components. The percentage amount of the deionized water contained therein corresponds to the difference from the sum of the amounts given in the table to a total of 100% by weight.

(8) a) Binders used (polymer dispersions/suspensions)

(9) 1. Dispersion A

(10) Nonionically stabilized polyepoxy dispersion with a solids content of 45% to 49%, a pH of 5.0 to 6.0, a viscosity of 1000-2000 mPas, an epoxy equivalent of 2300-2800 and a density of 1.1 g/cm.sup.3.

(11) 2. Dispersion B

(12) Nonionically stabilized polyurethane dispersion with a solids content of 30%, a pH of 3.0-6.0, a viscosity of 300-2000 mPas and a density of 1.1 g/cm.sup.3.

(13) 3. Dispersion C

(14) Ionically stabilized polyacrylate dispersion with a solids content of 50%, a pH of 7.5-8.5, a viscosity of 200 mPas, a density of 1.05 g/cm.sup.3.

(15) b) Gelling agents used

(16) 1. Gelling Agent A

(17) A 1:1 mixture of a polysaccharide with a molecular weight of approximately 70,000 g/mol, a degree of amidation of 11%, a degree of esterification of 10%, a degree of epoxidation of 0%, a galacturonic acid content of 88% and a polysaccharide with a molecular weight of approximately70,000 g/mol, a degree of amidation of 0%, a degree of esterification of 38%, a degree of epoxidation of 0%, a galacturonic acid content of 85% was used as the gelling agent. To prepare the formulation, a 2% aqueous solution of the polysaccharide was used.

(18) 2. Gelling Agent B

(19) A polysaccharide with a molecular weight of approximately 70,000 g/mol, a degree of amidation of 0%, a degree of esterification of 15%, a degree of epoxidation of 0%, a galacturonic acid content of 85% was used as the gelling agent. To prepare the formulation, a 2% aqueous solution of the polysaccharide was used.

(20) c) Pigments 1. Gas black-RCC pigment paste based on a dispersion resin for applications in aqueous coating systems with pH values in the acidic range with a pigment content of 4%, a filler content of 50%, a 10% dispersion additive content with a resulting solids content of approximately 60% 2. Micronized white pigment based on a titanium dioxide rutile, organically and inorganically coated 3. Iron oxide red, opaque, in an aqueous dispersion with color index of pigment red 101/77 491 with a pH of 7-10 and a density of 1.7 to 1.9 g/cm.sup.3 4. Cu phthalocyanine, alpha, in aqueous dispersion, a color index of pigment blue 15:2/74 160 with a pH of 7-10 and a density of 1.1 to 1.3 5. Quinophthalone yellow, a readily flowing paste with a color index of pigment yellow 138/56 300 with a pH of 7-10 and a density of 1.3-1.4

(21) d) Additives 1. Fluoride-containing aqueous pretreatment solutions—were not used when substrates with pretreatments (see point II) were used. Preferably used for deposition on aluminum substrates 2. Phosphoric acid as an aqueous solution (20%) 3. Foam suppressant, based on natural oils, emulsifiers and a 1% by weight content of the as-delivered form in water. The data given in the table are based on the amount of solution of liter of formulation.

(22) Additives were preferably used when the formulations had to be adapted to the pH or foaming was observed.

(23) Overview of the formulations used as examples.

(24) TABLE-US-00001 TABLE 1 Formulation examples of the coating and coating sequence according to the invention. Gelling Binder agent Pigment No. 1 2 3 1 2 1 2 3 4 5 pH 1 43.0 25.0 7.0 5.0 2 67.0 25.0 7.0 5.5 3 40.0 25.0 7.0 6.5 4 43.0 25.0 7.0 4.0 5 67.0 25.0 7.0 4.5 6 40.0 25.0 7.0 5.5 7 14.3 22.3 13.3 25.0 7.0 5.5 8 14.3 22.3 13.3 25.0 7.0 4.5 9 43.0 25.0 5.0 5.5 10 67.0 25.0 5.0 6.0 11 40.0 25.0 5.0 6.5 12 43.0 25.0 5.0 5.0 13 67.0 25.0 5.0 5.5 14 40.0 25.0 5.0 6.0 15 14.3 22.3 13.3 25.0 5.0 6.0 16 14.3 22.3 13.3 25.0 5.0 6.0 17 43.0 25.0 1.0 5.2 18 67.0 25.0 1.0 5.7 19 40.0 25.0 1.0 6.7 20 43.0 25.0 1.0 4.2 21 67.0 25.0 1.0 4.7 22 40.0 25.0 1.0 5.7 23 14.3 22.3 13.3 25.0 1.0 5.7 24 14.3 22.3 13.3 25.0 1.0 4.7 25 43.0 25.0 2.0 5.2 26 67.0 25.0 2.0 5.7 27 40.0 25.0 2.0 6.7 28 43.0 25.0 2.0 4.2 29 67.0 25.0 2.0 4.7 30 40.0 25.0 2.0 5.7 31 14.3 22.3 13.3 25.0 2.0 5.7 32 14.3 22.3 13.3 25.0 2.0 4.7 33 43.0 25.0 3.0 5.2 34 67.0 25.0 3.0 5.7 35 40.0 25.0 3.0 6.7 36 43.0 25.0 3.0 4.2 37 67.0 25.0 3.0 4.7 38 40.0 25.0 3.0 5.7 39 14.3 22.3 13.3 25.0 3.0 5.7 40 14.3 22.3 13.3 25.0 3.0 4.7
E. Rinsing the Organic Coating:

(25) Rinsing after the organic coating serves to remove any non-adhering constituents of the formulation and accumulations of the formulation and to make the process as close to reality as possible as is customary for industrial applications.

(26) F. Drying and Crosslinking the Coating:

(27) Drying or drying with formation of a film, wherein film forming in the sense of the present invention is also understood to refer to baking or crosslinking the coating, in particular the organic polymer ingredients.

(28) 1. 200° C. for 20 minutes

(29) Examples of the Coating Sequence

(30) The following coating sequences on substrate 2 are given here as examples, although the invention is not limited to these examples:

Example 1

(31) Step I

(32) Step II for 120 s with formulation no. 9 (15 μm dry film thickness)

(33) Step III for 15 s

(34) Step II for 60 s with formulation no. 1 (5 μm dry film thickness)

(35) Step III for 15 s

(36) Step II for 80 s with formulation no. 10 (10 μm dry film thickness)

(37) Step III for 15 s

(38) Step II for 60 s with formulation no. 4 (5 μm dry film thickness)

(39) Step III for 15 s

(40) Step II for 60 s with formulation no. 11 (5 μm dry film thickness)

(41) Step III for 15 s

(42) Drying and forming of film of the coating at 170° C. for 10 minutes. A five-layer coating is obtained by using the three binders listed as examples in the different layers. The coating is clearly differentiable visually due to the pigment additives.

Example 2

(43) Step I

(44) Step II for 180 s with formulation no. 15 (20 μm dry film thickness)

(45) Step III for 15 s

(46) Step II for 60 s with formulation no. 7 (20 μm dry film thickness)

(47) Step III for 15 s

(48) Step II for 80 s with formulation no. 16 (20 μm dry film thickness)

(49) Step III for 15 s

(50) Drying and forming of film from the coating at 170° C. for 10 minutes. A three-layer coating that is clearly differentiable visually due to the pigment additives is obtained.

Example 3

(51) Step I

(52) Step II for 180 s with formulation no. 3 (20 μm dry film thickness)

(53) Step III for 15 s

(54) Step II for 60 s with formulation no. 11 (20 μm dry film thickness)

(55) Step III for 15 s

(56) Step II for 80 s with formulation no. 3 (20 μm dry film thickness)

(57) Step III for 15 s

(58) Drying and forming of film of the coating at 170° C. for 10 minutes. A three-layer coating of approximately 60 μm that is clearly differentiable visually due to the pigment additives is obtained.