PROCESS FOR CORROSION-PROTECTING PRETREATMENT OF A METALLIC SURFACE CONTAINING STEEL, GALVANIZED STEEL, ALUMINUM, AN ALUMINUM ALLOY, MAGNESIUM AND/OR A ZINC-MAGNESIUM ALLOY

Abstract

Described herein is an improved process for anticorrosion pretreatment of a metallic surface including steel, galvanized steel, aluminum, an aluminum alloy, magnesium and/or a zinc-magnesium alloy, wherein the metallic surface is brought into contact with i) an acidic aqueous composition A which includes a1) at least one compound selected from the group consisting of titanium, zirconium and hafnium compounds, and with ii) an aqueous composition B which includes b1) at least one (meth)acrylate resin and b2) at least one phenol resin, where the metallic surface is brought into contact firstly with the composition A and then with the composition B and/or firstly with the composition B and then with the composition A and/or simultaneously with the composition A and the composition B.

Claims

1. A process for anticorrosion pretreatment of a metallic surface comprising steel, galvanized steel, aluminum, an aluminum alloy, magnesium and/or a zinc-magnesium alloy, wherein the metallic surface is brought into contact with i) an acidic aqueous composition A which comprises a1) at least one compound selected from the group consisting of titanium, zirconium and hafnium compounds, and ii) an aqueous composition B which comprises b1) at least one (meth)acrylate resin and b2) at least one phenolic resin, wherein the metallic surface is brought into contact i) firstly with the composition A and then with the composition B, ii) firstly with the composition B and then with the composition A, and/or iii) simultaneously with the composition A and the composition B.

2. The process according to claim 1, wherein the metallic surface is brought into contact firstly with the composition A and then with the composition B.

3. The process according to claim 1, wherein the at least one (meth)acrylate resin b1) is a copolymer of a methacrylic ester and acrylic acid.

4. The process according to claim 3, wherein the at least one (meth)acrylate resin b1) is a copolymer of a methyl methacrylate and acrylic acid.

5. The process according to claim 4, wherein the at least one (meth)acrylate resin b1) comprises 80 to 98% by weight of methyl methacrylate and 2 to 20% by weight of acrylic acid (total: 100% by weight), preferably 85 to 95% by weight of methyl methacrylate and 5 to 15% by weight of acrylic acid (total: 100% by weight).

6. The process according to claim 1, wherein the at least one (meth)acrylate resin b1) comprises hydroxyl, silyl, alkyl, aryl, heteroalkyl, heteroaryl, thio, amino, amide, nitrile, epoxy, mercapto, ureido, nitro, halo and/or cyano groups.

7. The process according to claim 1, wherein the at least one (meth)acrylate resin b1) has a mass-average molecular weight in the range of 1000 to 500 000 g/mol.

8. The process according to claim 1, wherein the at least one phenol resin b2) is a resole.

9. The process according to claim 1, wherein the at least one phenol resin b2) has a mass-average molecular weight in the range of 100 to 5000 g/mol.

10. The process according to claim 1, wherein the composition B comprises the at least one (meth)acrylate resin b1) and the at least one phenolic resin b2) in a weight ratio in the range of 1:1 to 10:1.

11. The process according to claim 1, wherein the concentration of the at least one (meth)acrylate resin b1) and the at least one phenolic resin b2) in total in the composition B is in the range of 20 to 400 mg/l (calculated as solid addition).

12. The process according to claim 1, wherein the composition B comprises as a stabilizer b3) at least one triblock copolymer of a formula I:
PEOx-PPOy-PEOz(I), where x and z in each case are an integer in the range of 4 to 12 and y is an integer in the range of 35 to 65.

13. The process according to claim 12, wherein a mass concentration (calculated as solid addition) of the stabilizer b3) in the composition B is in the range of 1.5 to 2.5 times the total concentration of the at least one (meth)acrylate resin b1) and the at least one phenol resin b2).

14. The process according to claim 1, wherein the composition B additionally comprises at least one compound b4) of a formula II:
R.sup.1O(CH.sub.2).sub.xZ(CH.sub.2).sub.yOR.sup.2(II), where R.sup.1 and R.sup.2 in each case independently of one another are H or a group HO(CH.sub.2).sub.w with w2, x and y in each case independently of one another are 1 to 4, and Z is a sulfur atom or a CC triple bond.

15. The process according to claim 1, wherein the composition B additionally comprises at least one molybdenum compound b5).

16. The process according to claim 1, wherein the at least one compound a1) in the composition A is at least one complex fluoride selected from the group consisting of the complex fluorides of titanium, zirconium and hafnium.

17. The process according to claim 1, wherein the composition A additionally comprises a2) at least one compound selected from the group consisting of organoalkoxysilanes, organosilanols, polyorganosilanols, organosiloxanes and polyorganosiloxanes.

18. The process according to claim 17, wherein the at least one compound a2) is at least one organoalkoxysilane, organosilanol, polyorganosilanol, organosiloxane and/or polyorganosiloxane having in each case at least one amino group, urea group, imido group, imino group and/or ureido group per organoalkoxysilane/organosilanol unit.

19. The process according to claim 1, wherein the composition A additionally comprises from 0.1 to 5 g/l of zinc cations, from 5 to 50 mg/l of copper cations and/or from 5 to 50 mg/l of cerium cations and/or from 10 to 100 mg/l of at least one molybdenum compound (calculated as molybdenum) as a component a3).

20. The process according to claim 1, wherein the metallic surface comprises steel and/or galvanized steel.

21. An aqueous composition B for improving the anticorrosion pretreatment of a metallic surface comprising steel, galvanized steel, magnesium and/or a zinc-magnesium alloy according to claim 1.

22. A concentrate, wherein a composition B according to claim 21 can be produced therefrom by dilution with water.

23. A metallic surface comprising steel, galvanized steel, magnesium and/or a zinc-magnesium alloy, wherein the metallic surface has been coated by a process according to claim 1 and a coating formed has a layer weight determined by means of XRF of: i) from 5 to 500 mg/m.sup.2 based only on the at least one compound a1) (calculated as zirconium) and optionally ii) from 0.5 to 50 mg/m.sup.2 based only on the at least one compound a2) (calculated as silicon).

24. A method for using a metallic substrate which has been coated by a process according to claim 1, the method comprising utilizing the metallic substrate in the automobile industry, for rail vehicles, in the aerospace industry, in apparatus construction, in mechanical engineering, in the building industry, in the furniture industry, for the production of crash barriers, lamps, profiles, cladding or small parts, for the production of bodywork or bodywork parts, of individual components, preinstalled or joined elements, in the aviation industry, or for the production of apparatuses or plants.

Description

EXAMPLES

i) Substrates and Pretreatments:

Substrates:

[0111] Sheets (10.519 cm) made of hot-dip galvanized steel (HDG) and others made of cold-rolled steel (CRS) were used as substrates.

Cleaning:

[0112] In all examples, Gardoclean S 5176 (from Chemetall; contains phosphate, borate and surfactant) was used as mild-alkaline dipping cleaner. For this purpose, 15 g/l were made up in a 50 l bath, heated to 60 C. and the substrates were cleaned by spraying for 3 minutes at a pH in the range from 10.0 to 11.0. The substrates were subsequently rinsed with mains water and deionized water.

Prerinse (According to the Invention):

[0113] The prerinse was carried out using deionized water to which different amounts of a resin mixture (cf. Tab. 1: Resin mix.) had optionally be added according to the invention. This resin mixture contained the following resole (exemplary formula) with a mass-average molecular weight of 160 g/mol

##STR00001##

and a (meth)acrylate resin with a mass-average molecular weight of 9630 g/mol (determined by means of GPC), which had been polymerized from 90 mol % methyl methacrylate and 10 mol % acrylic acid, in a weight ratio of 1:3.7.

[0114] Added optionally as well to the prerinse according to the invention was a mixture of corrosion inhibitors (cf. Tab. 1: Corr. inh.), so that the prerinse contained 62.5 mg/l of but-2-yne-1,4-diol and 50 mg/l of 1,4-bis(2-hydroxyethoxy)-2-butyne, giving a total of 112.5 mg/l of corrosion inhibitors.

TABLE-US-00001 TABLE 1 Prerinse Resin mix. (mg/l)* Corr. inh. (mg/l) A 0 0 B 50 0 C 200 0 D 50 112.5 *Solids content

[0115] The prerinse of the substrates was carried out for 120 seconds at 20 C. with moderate stirring.

Conversion Bath (According to the Invention):

[0116] For the conversion bath, the Oxsilan additive 9936 (from Chemetall, Germany; contains fluoride and a zirconium compound) and optionally Oxsilan 9810/3 (from Chemetall, Germany; contains aminosilanes, cf. Tab. 3: Silane) was or were added to a 50 l batch in such an amount that a zirconium concentration of 100-130 mg/l and a silane concentration of 20-30 mg/l (calculated as Si) resulted. The bath temperature was set to 30 C. The pH and the free fluoride content were set to pH=4.8 and 30-40 mg/l, respectively, by addition of dilute sodium hydrogencarbonate solution and dilute hydrofluoric acid (5% strength).

[0117] The pH was corrected continuously by addition of dilute nitric acid.

[0118] Added to the bath optionally according to the invention were various amounts of the resin mixture already described in connection with the prerinse according to the invention (cf. Tab. 3: Resin mix.).

[0119] Additionally added to the conversion bath according to the invention were various amounts of the specific triblock copolymer PEO.sub.8PPO.sub.50-PEO.sub.8 (Pluronic PE 9200; from BASF, Germany, cf. Tab. 3: Stabil.).

[0120] The bath (according to the invention) always also contained 400 mg/l of zinc. Added optionally to the bath (according to the invention) were 8-10 mg/l of copper in the form of copper nitrate.

[0121] Before substrates were passed through, the finished bath was left to age for at least 12 hours in order to be able to ensure establishment of a chemical equilibrium within the bath. The conversion treatment was carried out for 120 seconds with moderate stirring. Rinsing with mains water and deionized water was subsequently carried out.

Afterrinse According to the Invention:

[0122] For the afterrinse, deionized water was used to which optionally, according to the invention, various amounts of the resin mixture already described in connection with the prerinse according to the invention (cf. Tab. 2: Resin mix.) and also, optionally, 100 mg/l of the specific triblock copolymer already described in connection with the conversion bath according to the invention (cf. Tab. 2: Stabil.) were added.

[0123] Added optionally to the afterrinse were also 20 mg/l or 50 mg/l of molybdenum in the form of ammonium heptamolybdate.

TABLE-US-00002 TABLE 2 Afterrinse Resin mix. (mg/l)* Stabil. (mg/l)* Mo (mg/l) A 0 0 0 B 50 0 0 C 200 0 0 D 400 0 0 E 50 100 0 F 50 100 20 G 50 100 50 *Solids content

[0124] The substrates were afterrinsed with moderate stirring at 20 C. for 90 seconds.

[0125] The combination of the various prerinses, conversion baths and afterrinses produced the examples and comparative examples set out in Tab. 3 below:

TABLE-US-00003 TABLE 3 Conversion bath Resin (Comp.) Zr Si Cu mix. Stabil. Ex. Subs. Prerinse (mg/l) (mg/l)* (mg/l) (mg/l)** (mg/l)** Afterrinse CE1 HDG A 120 30 8 0 0 A E2 HDG A 120 30 8 15 0 A E3 HDG A 130 30 10 20 40 A E4 HDG A 130 30 10 50 100 A E5 HDG A 130 30 10 70 140 A E6 HDG A 130 30 10 50 100 A E7 HDG A 130 30 10 100 200 A CE8 CRS A 120 30 8 0 0 A E9 CRS A 130 30 10 20 40 A E10 CRS A 130 30 10 50 100 A E11 HDG A 120 30 8 0 0 B E12 HDG A 130 30 10 0 0 B E13 HDG A 130 30 10 0 0 D E14 HDG A 130 30 10 0 0 B E15 HDG A 130 30 10 0 0 C E16 HDG A 130 30 0 0 0 C E17 CRS A 130 0 0 0 0 C E18 CRS A 130 30 0 0 0 C E19 CRS C 130 30 10 0 0 A E20 HDG B 130 30 10 0 0 A E21 HDG C 130 30 10 0 0 A E22 HDG D 130 30 10 0 0 A E23 HDG A 120 30 8 30 0 A E24 CRS A 130 30 10 100 200 A E25 HDG A 120 30 8 27.5 0 A E26 CRS A 120 30 8 27.5 0 A CE27 HDG A 100 30 8 0 0 A E28 HDG A 100 30 8 0 0 E E29 HDG A 100 30 8 0 0 F E30 HDG A 100 30 8 0 0 G *Calculated as Si; **Solids content

ii) Analysis, Coating, Bond Strength and Corrosion Protection:

X-Ray Fluorescence Analysis:

[0126] The layer weights (LW) in mg/m.sup.2 on the pretreated substrates were determined by means of X-ray fluorescence analysis (XRF). Here, the amount of zirconium applied was measured.

Surface Coating:

[0127] The pretreated substrates were coated by CEC. Cathoguard 800 (from BASF Germany) was used for this purpose. A buildup coating was subsequently applied. This was Daimler Black. The thickness of the coating layer was determined by means of a layer thickness measuring instrument in accordance with DIN EN ISO 2808 (2007 version). It was in the range from 90 to 110 m.

Corrosion Tests:

[0128] In addition, four different corrosion tests were carried out:

1.) the corrosion cycle test according to Volkswagen specification PV 1210 (2010 February version) over 60 rounds,
2.) the corrosion cycle test according to VDA test sheet 621-415 and according to DIN EN ISO 20567-1 (1982 version method C) over 10 rounds,
3.) the corrosion cycle test Meko S test c in accordance with DIN EN ISO 4628-8 (2013 March version), and
4.) the cathodic polarization in accordance with FFM_C-AN_01941 (2.0 version)

Delamination:

[0129] The corrosive delamination in mm was in each case determined in accordance with DIN EN ISO 4628-8 (2012 version) (cf. Tab. 4: Cd). The values reported are average values from three sheets in each case.

[0130] The results of the corrosion tests carried out are summarized in Tab. 4 below:

TABLE-US-00004 TABLE 4 (Comp. LW (Zr) VDA 621-415 PV 1210 Meko S Cath. Pol. Ex. (mg/m.sup.2) Cd (mm) Cd (mm) Cd (mm) Cd (mm) CE1 94 2.3 3.0 5.8 n.d. E2 80 1.8 2.4 n.d. n.d. E3 117 1 n.d. n.d. n.d. E4 119 0.8 n.d. n.d. n.d. E5 115 1 n.d. n.d. n.d. E6 62 0.8 n.d. n.d. n.d. E7 59 0.9 n.d. n.d. n.d. CE8 50 2.8 5.2 5.3 n.d. E9 51 1.6 n.d. n.d. n.d. E10 50 1.7 n.d. n.d. n.d. E11 90 1.8 n.d. 4.8 n.d. E12 125 1 n.d. n.d. n.d. E13 147 1.2 n.d. n.d. n.d. E14 69 0.8 n.d. n.d. n.d. E15 70 0.7 n.d. n.d. n.d. E16 46 0.8 n.d. n.d. n.d. E17 81 1.2 n.d. n.d. n.d. E18 53 1.0 n.d. n.d. n.d. E19 30 1 n.d. n.d. n.d. E20 66 1 n.d. n.d. n.d. E21 45 0.8 n.d. n.d. n.d. E22 60 0.8 n.d. n.d. n.d. E23 97 n.d. 2.4 n.d. n.d. E24 27 n.d. 2.7 n.d. n.d. E25 113 n.d. n.d. 4.6 n.d. E26 48 n.d. n.d. 4.9 n.d. CE27 86 n.d. n.d. n.d. 12.8 E28 93 n.d. n.d. n.d. 11.5 E29 74 n.d. n.d. n.d. 5.4 E30 79 n.d. n.d. n.d. 3.9 n.d. = not determined
iii) Results and Discussion:

[0131] Tab. 4 shows that through addition of the resin mixture according to the invention, in the prerinse, in the conversion bath and in the afterrinse, a reduction can be ascertained in the corrosive delamination (cf. values of the examples versus those of the comparative examples CE1, CE8 and CE27).

[0132] Through the addition of silane there is again an improvement (cf. E18 versus E17). The addition of copper results in an increase in the layer weight (cf. E15 and E16).

[0133] Though the addition of the specific triblock copolymer, a distinct increase was posted (results not shown) in the useful life of the conversion bath comprising the resin mixture according to the invention. Agglomeration of the resin in the acidic environment was very largely prevented (E3 to E7 versus E2; E9 and E10).

[0134] The addition of the corrosion inhibitor to the prerinse according to the invention likewise resulted in a further improvement (cf. E22 versus E20), as did the addition of molybdenum to the afterrinse according to the invention (cf. E29, E30 versus E29).