PRE-RINSE CONTAINING A QUATERNARY AMINE FOR CONDITIONING PRIOR TO A CONVERSION TREATMENT

Abstract

A multi-step process for the anti-corrosive pretreatment of components component formed at least partially from metallic materials wherein first components are subjected to a conditioning wet-chemical treatment with an aqueous composition (A) that contains a salt of a quaternary amine and then to an additional wet-chemical treatment based on water-soluble compounds of the elements Zr, Ti and/or Si, in the course of which treatment a corresponding conversion of the surfaces of the metallic materials takes place, said treatment providing an anti-corrosive primer for additionally applied organic coatings.

Claims

1. A multi-stage method for anti-corrosive pretreatment of components fabricated at least partially from metallic materials, wherein initially: i) at least a portion of a surface of a component formed at least partially from metallic materials is brought in contact with an aqueous composition (A) comprising a dissolved and/or dispersed salt of a quaternary organic amine; and subsequently ii) at least the same portion of the surface of the component formed at least partially from the metallic materials is brought in contact with an aqueous composition (B) comprising one or more water-soluble compounds of the elements Zr, Ti and/or Si.

2. The method according to claim 1, wherein the quaternary organic amines are selected from heterocyclic compounds comprising at least one quaternary nitrogen heteroatom.

3. The method according to claim 2, wherein the heterocyclic compound comprising at least one quaternary nitrogen heteroatom corresponds to the following chemical formula (I): ##STR00002## wherein functional groups R.sup.1, R.sup.2 and R.sup.3 are each independently selected from hydrogen; branched or unbranched aliphatic compounds comprising no more than 6 carbon atoms; and a functional group corresponding to:
C(CR.sub.4R.sub.4).sub.x[Z(R.sub.4).sub.(p-1)(CR.sub.4R.sub.4).sub.y].sub.nZ(R.sub.4).sub.p where Z is selected from oxygen or nitrogen; p, in cases where Z is nitrogen, is 2 and otherwise is equal to 1; x and y are each natural numbers from 1 to 4; n is a natural number from 0 to 4; and R.sup.4 is selected from hydrogen, branched aliphatic compounds comprising no more than 6 carbon atoms and unbranched aliphatic compounds comprising no more than 6 carbon atoms; with the proviso that at least one of the functional groups R.sup.2 or R.sup.3 is not selected from hydrogen; and Y is a ring-constituting divalent functional group, which comprises no more than 5 bridge atoms, wherein no more than one heterobridge atom different from carbon atoms selected from oxygen, nitrogen or sulfur can be a bridge atom, and the carbon atoms in turn independently of one another are present substituted with functional groups R.sup.1 or with functional groups via which an annulation of aromatic homocyclic compounds having no more than 6 carbon atoms is achieved.

4. The method according to claim 3, 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-butadienediyl, CHN, CH.sub.2NH, (N,N-dimethylene)amine, (N-methylene-N-methylylidene)amine, wherein in each case hydrogen covalently bound to a carbon atom can be substituted by the remaining representatives of functional group R.sup.1.

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

6. The method according to claim 1, wherein the quaternary organic amine is selected from 1,2,3-trimethylimidazolium, 1-methyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-isopropyl-3-methylimidazolium, 1-propyl-3-methylimidazolium, 1-(n-butyl)-3-methylimidazolium, 1-(isobutyl)-3-methylimidazolium, 1-methoxy-3-methylimidazolium, 1-ethoxy-3-methylimidazolium, 1-propoxy-3-methylimidazolium and mixtures thereof.

7. The method according to claim 1, wherein the aqueous composition (A) in step i) additionally comprises anions comprising no more than 5 carbon atoms and selected from monoalkyl sulfates, monoalkyl sulfonates, dialkyl phosphates and/or dialkyl phosphonates.

8. The method according to claim 1, wherein the quaternary organic amine in the aqueous composition (A) is present in an amount of at least 0.05 g/kg, but no more than 20 g/kg.

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

10. The method according to claim 1, wherein the aqueous composition (A) comprises less than 0.05 g/kg of surface-active compounds which are not composed of quaternary organic amines.

11. The method according to claim 1, wherein the aqueous composition (B) in step ii) comprises at least 0.01 g/kg of water-soluble compounds of the elements Zr, Ti or Si, based on the respective element.

12. The method according to claim 1, wherein the aqueous composition (B) in step ii) comprises less than 0.05 g/kg free fluoride.

13. The method according to claim 1, wherein a total proportion of fluorides in the aqueous composition (B) in step ii) is less than 0.05 g/kg.

14. The method according to claim 1, further comprising cleaning and degreasing the component formed at least partially from metallic materials prior to step i), by bringing the component into contact with aqueous compositions comprising surface-active compounds.

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

16. The method according to claim 1, wherein the component formed at least partially from metallic materials at least partially comprises surfaces of iron and/or steel, and at least 50%, of the surface of metallic materials of the component is formed of surfaces of the materials iron and/or steel.

17. The method according to claim 5, wherein the quaternary organic amine is selected from 1,2,3-trimethylimidazolium, 1-methyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-isopropyl-3-methylimidazolium, 1-propyl-3-methylimidazolium, 1-(n-butyl)-3-methylimidazolium, 1-(isobutyl)-3-methylimidazolium, 1-methoxy-3-methylimidazolium, 1-ethoxy-3-methylimidazolium, 1-propoxy-3-methylimidazolium and mixtures thereof.

18. The method according to claim 17, wherein the aqueous composition (A) in step i) additionally comprises anions selected from monoalkyl sulfates and/or monoalkyl sulfonates, said anions comprising no more than 5 carbon atoms.

Description

EXEMPLARY EMBODIMENTS

[0049] Hereafter, sheets made of steel (CRS) are subjected to a multi-stage process for anti-corrosive pretreatment. The suitability of metal sheets thus pretreated and provided with a paint coat to serve as a good paint primer is examined in a test according to DIN EN ISO 4628-8 for corrosive delamination.

[0050] The general method for pretreatment and coating comprises the successive mandatory and optional individual steps (A) to (E): [0051] (A) Alkaline cleaning and degreasing: [0052] immersing the sheet, while stirring, in an alkaline cleaning agent composed of 4 wt. % Ridoline 2011 (Henkel) and 0.4 wt. % Ridosol 1270 (Henkel) for 5 minutes at 56 C.; [0053] (B) rinsing with process water and then with deionized water (<1 Scm.sup.1), each at 20 C.; [0054] (C) conditioning by immersing the sheet for 1 minute at 35 C. in a composition comprising a predefined amount of a conditioner in deionized water (<1 Scm.sup.1), without adding further pH-changing substances; [0055] (D) if necessary, rinsing with deionized water at 20 C. (<1 Scm.sup.1); [0056] (E) carrying out a conversion treatment by immersing the sheet for 3 minutes at 35 C. in an aqueous composition having a pH value of approximately 2.6, containing 1.6 g/kg ZrO(NO.sub.3).sub.2.

[0057] Table 1 below shows the different organic compounds used in the conditioning in step (C).

TABLE-US-00001 TABLE 1 Compositions used in conditioning: Conditioner Amount in pH g/kg Anion Cation value C1 2 4.3 C2 2.5 Chloride 1-ethyl-3- 5.5 methylimidazolium C3 2.5 Methyl sulfate 1,2,3-trimethylimidazolium 7.5 *Polyvinylpyrrolidone (Mw~160,000 g/mol)

[0058] Subsequent to the conversion treatment in method step (E), the respective sheet was first rinsed with deionized water (<1 Scm.sup.1) at 20 C. and then coated with a cataphoretic paint and dried at 180 C. (dry layer thickness: 18 to 20 m; CathoGuard 800 from BASF Coatings).

[0059] It is apparent from a review of the results of Table 2 that, on steel sheets, a coat structure in the range of 0 to 20 mg/m.sup.2 zirconium cannot be reproducibly implemented in step (D) in the experiment for carrying out a conversion treatment solely based on a fluoride-free composition (No. 1). Conditioning based on a pretreatment using an aqueous solution comprising polyvinylpyrrolidone (No. 2) likewise fails since the conversion layer formation takes place neither at an increased level nor reproducibly as a whole.

[0060] Only when imidazolium salts are added is a significant conversion of the steel surfaces achieved, so that a coating weight in the range of 15 to 60 m.sup.2, which is usually sufficient for good corrosion protection and serving as a good paint primer, is achieved (Nos. 3 and 4). If methyl sulfate anions are additionally present, moreover strong acceleration of the conversion layer formation is observed (No. 5).

[0061] The corrosion results and the respective associated process sequence are provided in Table 2.

TABLE-US-00002 TABLE 2 Corrosion results on the appropriately pretreated and electrophoetically coated sheets Process Corrosion.sup.1 Coat structure.sup.2 Zr No. sequence U2/mm mg/m.sup.2 1 A-B-D-E 3.3 10 10 # 2 A-B-C1-D-E 33 6 5 3 A-B-C2-D-E 2.5 15 3 4 A-B-C3-D-E 2.2 57 9 .sup.1Corrosion at the cut according to DIN EN ISO 4628-8,after aging in the V W alternating climate test according to PV 12103. .sup.2Mean value and standard deviation across 5 sheets, wherein the averaged value from 6 individual measurements for the same sheet is used for the coat structure of each individual sheet, and the determination was made by way of an X-ray fluorescence analyzer Niton XL3t 900 (Thermo Fisher Scientific) using an analysis surface of 50 mm.sup.2. # Mean value and standard deviation across 62 sheets.