Polymer-containing pre-rinse prior to a conversion treatment

Abstract

A multi-step method for anti-corrosion pretreatment of components made from metallic materials, in which a wet chemical treatment with an aqueous composition (A) containing a dissolved and/or dispersed polymer P, which is substituted with heterocycles containing at least one quaternary nitrogen heteroatom, is followed by a conversion treatment based on water-soluble compounds of the elements Zr, Ti, and/or Si before further anti-corrosion coatings are optionally applied.

Claims

1. A multi-step method for anti-corrosion pretreatment of components made at least in part from metallic materials, comprising steps of: i) initially contacting at least a portion of surfaces of the components made at least in part from metallic materials with an aqueous composition (A) containing a dissolved and/or dispersed organic polymer P, of which a weight proportion of at least 40%, based on the total proportion of said organic polymer P is made up of repeating units R.sub.N which comprise as a substituent a heterocycle containing at least one quaternary nitrogen heteroatom; and subsequent to step i), with or without a rinsing and/or drying step therebetween; ii) bringing at least the portion of the surfaces of the components made at least in part from metallic materials into contact with an acidic aqueous composition (B) containing one or more water-soluble compounds of the elements Zr, Ti, and/or Si.

2. The method according to claim 1, wherein the repeating units R.sub.N of the polymer P, which have the heterocycle containing at least one quaternary nitrogen heteroatom, have a structural element which corresponds to the following structural formula (I): ##STR00003## where R.sup.1 is selected from hydrogen, branched or unbranched aliphatic functional groups having no more than 6 carbon atoms, and a functional group —(CR.sup.4R.sup.4).sub.x—[Z(R.sup.4).sub.(p−1)—(CR.sup.4R.sup.4).sub.y].sub.n—Z(R.sup.4).sub.p, where Z is in each case selected from oxygen or nitrogen; p, where Z is nitrogen, has the value 2 and otherwise is 1; x and y are each natural numbers independently ranging from 1 to 4; n is a natural number ranging from 0 to 4; and R.sup.4 is selected from hydrogen, and branched or unbranched aliphatic functional groups having no more than 6 carbon atoms; where Y is a ring-constituting divalent functional group having no more than 5 bridge atoms, and no more than one hetero bridge atom that is different from carbon atoms may be selected from an oxygen, nitrogen, or sulfur bridge atom, and the carbon atoms in turn are present substituted independently of one another with functional groups R.sup.1 or those functional groups via which annulation of aromatic homocyclen having no more than 6 carbon atoms is achieved.

3. The method according to claim 1, wherein the repeating units R.sub.N of the polymer P correspond to the following structural formula (II): ##STR00004## where R.sup.1 is selected from hydrogen; branched or unbranched aliphatic functional groups having no more than 6 carbon atoms; and a functional group —(CR.sup.4R.sup.4).sub.x—[Z(R.sup.4).sub.(p−1)—(CR.sup.4R.sup.4).sub.y].sub.n—Z(R.sup.4).sub.p, where Z is in each case selected from oxygen or nitrogen; p, where Z is nitrogen, has the value 2 and otherwise is 1; x and y are each natural numbers ranging from 1 to 4; n is a natural number ranging from 0 to 4, and R.sup.4 is selected from hydrogen; and branched or unbranched aliphatics having no more than 6 carbon atoms; where R.sup.2 and R.sup.3 are each independently selected from R.sup.1; and a remaining fragment of the repeating unit R.sub.N via which the repeating units R.sub.N are covalently bonded to one another or to other repeating units R.sub.X, provided that either R.sup.2 or R.sup.3 represents said remaining fragment of the repeating unit R.sub.N; and where Y is a ring-constituting divalent functional group having no more than 5 bridge atoms, and no more than one hetero bridge atom that is different from carbon atoms may be selected from an oxygen, nitrogen, or sulfur bridge atom, and the carbon atoms in turn are present substituted independently of one another with functional groups R.sup.1 or those functional groups via which annulation of aromatic homocyclen having no more than 6 carbon atoms is achieved.

4. The method according to claim 2, wherein the ring-constituting divalent functional group Y is selected from ethylene; ethenediyl; 1,3-propanediyl; 1,3-propenediyl; 1,4-butanediyl; 1,4-butenediyl; 1,4-butadiendiyl; —CH═N—; —CH.sub.2—NH—; (N,N-dimethylene)amine; and (N-methylene-N-methylylidene)amine.

5. The method according to claim 2, wherein the ring-constituting divalent functional group Y is selected from ethenediyl, 1,4-butadiendiyl, —C═N, and (N-methylene-N-methylylidene)amine.

6. The method according to claim 1, wherein the repeating unit R.sub.N is selected from 1-methyl-3-vinylimidazolium, 1-ethyl-3-vinylimidazolium, 1-isopropyl-3-vinylimidazolium, 1-propyl-3-vinylimidazolium, 1-(n-butyl)-3-vinylimidazolium, 1-(isobutyl)-3-vinylimidazolium, 1-methoxy-3-vinylimidazolium, 1-ethoxy-3-vinylimidazolium, and 1-propoxy-3-vinylimidazolium.

7. The method according to claim 1, wherein the polymer P contains at least one further repeating unit R.sub.X selected from vinylpyrrolidone, vinylcaprolactam, vinyl acetate, vinylimidazole, (meth)acrylic acid amide, (meth)acrylic acid, (meth)acrylic acid esters, and/or styrene.

8. The method according to claim 7, wherein the polymer P contains at least one further repeating unit R.sub.X selected from vinylpyrrolidone, vinylimidazole and/or (meth)acrylic acid amide.

9. The method according to claim 1, wherein the repeating units R.sub.N are present in a weight fraction of at least 80%, based on an overall fraction of the polymer P.

10. The method according to claim 1, wherein the polymer P is present in composition (A) in a proportion of at least 0.05 g/kg but not more than 2 g/kg.

11. The method according to claim 8, wherein the repeating unit R.sub.N is selected from an alkyl or alkoxy substituted 3-vinylimidazolium.

12. The method according to claim 11, wherein the repeating units R.sub.N are present in a weight fraction of at least 60%, based on an overall fraction of the polymer P.

13. The method according to claim 12, wherein the polymer P is present in composition (A) in a proportion of at least 0.1 g/kg but not more than 2 g/kg.

14. The method according to claim 1, wherein no conversion layer is created on the surfaces of the metallic components in step i).

15. The method according to claim 1, wherein the aqueous composition (A) contains less than 0.005 g/kg, in each case of water-soluble compounds of the elements Zr, Ti, and/or Si, based on the particular element; and composition (B) in step ii) contains a source of fluoride ions.

16. The method according to claim 1, wherein composition (B) in step ii) additionally contains water-soluble compounds that represent a source of copper ions.

17. The method according to claim 1, wherein no rinsing step takes place between steps i) and ii).

18. The method according to claim 1, wherein the surfaces of the components made at least in part from metallic materials are at least in part iron and/or steel surfaces.

19. The method according to claim 18, wherein in addition to iron and/or steel surfaces, the component also has surfaces of zinc and/or galvanized steel and/or surfaces of aluminum.

20. The method according to claim 19, wherein the surfaces of zinc and/or galvanized steel are present in the components and have an iron coverage of at least 20 mg/m.sup.2.

Description

EXEMPLARY EMBODIMENTS

(1) As described below, sheets of steel (CRS), galvanized steel (HDG), and aluminum were each independently subjected to a multi-step method for anti-corrosion pretreatment. The suitability of metal sheets, pretreated in this way and provided with a coating layer, for providing a good coating adhesion base was examined in respective material-specific corrosion tests.

(2) The general method for the pretreatment and coating is made up of the following successive mandatory and optional individual steps A)-E): A) Alkaline cleaning and degreasing: The sheet is immersed, with stirring, in an alkaline cleaner composed of 4% by weight Ridoline® 2011 (Henkel) and 0.5% by weight Ridosol® 1561 (Henkel) at 60° C. for 3 minutes for aluminum substrates, and at 60° C. for 5 minutes for steels and galvanized steels; B) Rinsing with process water and then with deionized water (κ<1 μScm.sup.−1) at 20° C. in each case; C) Conditioning by immersion of the sheet, with stirring, at 35° C. for 1 minute in a composition containing a predefined quantity of an organic polymer in deionized water (κ<1 μScm.sup.−1) without further additional of pH-modifying substances; D) Optionally rinsing with deionized water at 20° C. (κ<1 μScm.sup.−1); E) Conversion treatment by immersing the sheet, with stirring, at 35° C. for 3 minutes in an aqueous composition having a pH of 4.0, containing 0.34 g/kg of H.sub.2ZrF.sub.6 0.10 g/kg of CuSO.sub.4 3.0 g/kg of nitrate ions from sodium nitrate and a quantity of (NH.sub.4)HF.sub.2 sufficient for setting a free fluoride content of 23 mg/kg, measured with a fluoride-sensitive electrode at 20° C., using a potentiometric measurement chain (WTW, inoLab®, pH/ion level 3) containing a fluoride-sensitive glass electrode (WTW, F501) and a reference electrode (WTW, R503), and a three-point calibration is performed, using calibration solutions having a content of 10 mg/kg, 100 mg/kg, and 1000 mg/kg of free fluoride, prepared from the Merck Titrisol® fluoride standard without addition of buffer.

(3) After the conversion treatment in method step E), all sheets were initially rinsed with deionized water (κ<1 μScm.sup.−1) at 20° C., and subsequently coated with a cathodic dip coating and dried at 180° C. (dry layer thickness: 18-20 μm; CathoGuard® 800 from BASF Coatings).

(4) The various polymer-containing compositions used in the conditioning in step C) are shown in Table 1 below.

(5) TABLE-US-00001 TABLE 1 Compositions used in the conditioning; pH approximately 5.0-5.6 Polymer P Quantity in Molar ratio mg/kg Monomer (QVI:VP) C1 2000 1-Methyl-3-vinylimidazolium 95:5 (QVI); vinylpyrrolidone (VP) C2 1000 1-Methyl-3-vinylimidazolium 95:5 (QVI); vinylpyrrolidone (VP) C3 500 1-Methyl-3-vinylimidazolium 95:5 (QVI); vinylpyrrolidone (VP) C4 100 1-Methyl-3-vinylimidazolium 95:5 (QVI); vinylpyrrolidone (VP) C5 2000 1-Methyl-3-vinylimidazolium  30:70 (QVI); vinylpyrrolidone (VP) C6 1000 CELQUAT ® SC-240C — (AkzoNobel N.V.)

(6) The corrosion results and the particular associated method sequence are shown in Table 2. It is clear that, with regard to infiltration after aging in the alternating climate test and the stone chipping test, much better results were obtained on steel sheets in comparison to a strict conversion treatment (No. 9) when conditioning of the type of the present invention was carried out (Nos. 1-8). It was possible to obtain excellent corrosion protection results on steel and aluminum (compare No. 1 and No. 5) in particular for polymer-containing compositions in the conditioning C) in which the relative proportion of an heterocyclic structural units containing quaternary nitrogen atoms in the polymer was relatively high.

(7) Conversely, Example 9 demonstrates that not every polymer that bears substituents containing quaternary nitrogen atoms is able to provide successful conditioning of the metal surface for the subsequent conversion treatment. The polymer in the conditioning for Example 9 is a modified cellulose in which tetraalkylammonium structural units are bound to the cellulose basic structure via polyether bridges.

(8) The dependency of the conditioning on concentration shows a trend that in methods in which the conditioning is immediately followed by a rinse with deionized water, higher proportions of polymers are advantageous for maintaining good corrosion values on galvanized steel (compare No. 8 and No. 3, and No. 7 and No. 2). It may be concluded that for the steel substrates, a subsequent rinse with the same conditioning for corrosion protection is slightly advantageous (compare No. 8 and No. 3, and No. 7 and No. 2). The optimum for the substrate aluminum is independent of whether rinsing is carried out after the conditioning, preferably with average contents of the copolymers based on imidazolium (see No. 3 and No. 7).

(9) TABLE-US-00002 TABLE 2 Corrosion results on the correspondingly pretreated and dip-coated sheets CRS HDG AI.sup.4 Stone Stone Maximum Average No. Method sequence Corrosion.sup.1 Delamination.sup.2 chipping.sup.3 Corrosion.sup.1 Delamination.sup.2 chipping.sup.3 thread length thread length 1 A-B-C1-D-E 0.6 0.6 2.2 4.4 4.4 3.7 1.6 0.3 2 A-B-C2-D-E 0.5 0.5 2.5 4.7 4.7 4.0 1.6 0.2 3 A-B-C3-D-E 0.5 0.5 2.0 6.1 6.1 4.0 1.4 0.3 4 A-B-C4-D-E 0.6 0.6 2.3 5.0 5.0 3.8 1.7 0.3 5 A-B-C5-D-E 0.8 0.8 3.7 4.2 4.2 4.0 1.1 0.1 6 A-B-C1-E 0.6 0.6 2.3 4.2 4.2 3.8 2.9 0.7 7 A-B-C2-E 0.6 0.6 2.7 4.1 4.1 4.0 1.3 0.3 8 A-B-C3-E 0.6 0.6 2.8 3.8 3.8 3.7 1.7 0.2 9 A-B-C6-E 1.1 2.3 5.0 4.8 4.8 4.8 — — 10 A-B-E 1.0 1.3 3.0 4.4 4.4 4.2 1.4 0.1 .sup.1Average corrosion in mm according to DIN EN ISO 4628-8, after aging in the VW alternating climate test according to PV 1210 .sup.2Average delamination in mm according to DIN EN ISO 4628-8, after aging in the VW alternating climate test according to PV 1210 .sup.3Stone chipping test according to DIN EN ISO 20567-1, before and after aging in the VW alternating climate test according to PV 1210 .sup.4Thread lengths in mm according to Daimler PAPP PWT 3002, after aging in the filiform corrosion test according to DIN EN 3665