AQUEOUS SOLUTION AND METHOD FOR IMPROVING CORROSION RESISTANCE OF A CR(III) CONVERSION COATING AND MODIFIED CR(III) CONVERSION COATING

Abstract

This invention relates to an aqueous solution and a method for preparing an organic protective coating on a Cr(lll) conversion layer which is localized on (anodized) aluminium (alloy) to enhance corrosion protection. The composition is an aqueous solution which contains water, an organic film forming agent and a corrosion inhibitor, wherein the corrosion inhibitor comprises or consists of at least one 2-arylriazole. According to the method of the present invention, the composition is used for post-treating of a Cr(lll) conversion layer on (anodized) aluminium (alloy). The invention further provides a modified Cr(III) conversion coating on (anodized) aluminium (alloy), which is producible or produced with the inventive method. The modified Cr(III) conversion coating according to the invention shows excellent corrosion protection, paint adhesion and electrical resistivity.

Claims

1-15. (canceled)

16. An aqueous solution for improving corrosion resistance of a Cr(III)-conversion coating on aluminium, aluminium alloy, anodized aluminium and/or anodized aluminium alloy, comprising: a) a corrosion inhibitor; b) an organic film forming agent; and c) water; wherein the corrosion inhibitor comprises at least one 2-aryl-triazole.

17. The aqueous solution according to claim 16, wherein the concentration of the at least one 2-aryl-triazole is 0.5 to 50 g/L based on the total mass of the solution.

18. The aqueous solution according to claim 16, wherein the corrosion inhibitor comprises a mixture of a 2-aryl-triazole and a 2-aryl-alkyl-triazole.

19. The aqueous solution according to claim 18, wherein the 2-aryl-alkyl-triazole is selected from the group consisting of 2-aryl-1-alkyl-triazole, 2-aryl-3-alkyl-triazole, 2-aryl-4-alkyl-triazole, 2-aryl-5-alkyl-triazole, and any combination thereof.

20. The aqueous solution according to claim 16, wherein the organic film forming agent is selected from the group consisting of polymers comprising an acrylic group.

21. The aqueous solution according to claim 20, wherein the polymer comprising an acrylic group is selected from a polymer having an acrylic group selected from the group consisting of acrylonitrile, methacrylonitrile, methyl acrylate, methyl methacrylate, acrylate, methacrylate, acrylamide, methacrylamide, and any combination thereof.

22. The aqueous solution according to claim 16, wherein the concentration of the organic film forming agent is 1 to 100 g/L.

23. The aqueous solution according to claim 16, wherein the aqueous solution further comprises a wetting agent.

24. The aqueous solution according to claim 23, wherein the wetting agent is a siloxane-based wetting agent.

25. The aqueous solution according to claim 23, wherein the concentration of the wetting agent is 0.1 to 20 g/L based on the total mass of the solution.

26. The aqueous solution according to claim 16, wherein the solution does not comprise a compound having at least two hydroxy groups and/or does not comprise a compound having at least one carboxy group.

27. The aqueous solution according to claim 16, wherein the pH of the aqueous solution is from 4 to 14.

28. The aqueous solution according to claim 16, wherein the aluminium alloy is an aluminium-copper alloy.

29. A method for providing a modified Cr(III)-conversion coating on aluminium, an aluminium alloy, an anodized aluminium and/or an anodized aluminium alloy having a Cr(III)-conversion coating on the surface, wherein the method comprises contacting the Cr(III)-conversion coating with an aqueous solution according to claim 16.

30. The method according to claim 29, further comprising contacting the Cr(III)-conversion coating with an aqueous passivation solution.

31. The method according to claim 30, wherein the aqueous passivation solution comprises at least one 2-aryl-triazole.

32. The method according to claim 29, wherein, before contacting with the aqueous solution and/or before contacting with the passivation solution, at least one of the following steps is performed: i) contacting the aluminium, the aluminium alloy, the anodized aluminium and/or the anodized aluminium alloy with an aqueous, alkaline cleaning solution; ii) rinsing a cleaned aluminium, aluminium alloy, anodized aluminium and/or anodized aluminium alloy with water; iii) contacting the aluminium, aluminium alloy, anodized aluminium and/or anodized aluminium alloy with an aqueous deoxidizing solution; and iv) rinsing the aluminium, aluminium alloy, anodized aluminium and/or anodized aluminium alloy with water.

33. The method according to claim 29, wherein after contacting with the aqueous solution, at least one of the following steps is performed: i) rinsing the modified Cr(III)-conversion coating with water; and ii) drying the modified Cr(III)-conversion coating.

34. A modified Cr(III)-conversion coating on aluminium, aluminium alloy, anodized aluminium and/or anodized aluminium alloy, which is produced by the method according to claim 29.

Description

[0040] With reference to the following Figures and Examples, the subject according to the invention is intended to be explained in more detail without wishing to restrict said subject to the special embodiments shown here.

[0041] FIG. 1 shows the results of the corrosion resistance test (according to ISO 9227) of an aluminium 2024 panel treated with a conventional passivation solution (see recipe in Example 1) and treated or not treated with an inventive post-treatment solution (see recipe in Example 4). Illustrated are the number of pits that appeared after a certain amount of time after exposure to NSST. In addition, the results obtained for a known chromate conversion layer (Alodine 1200 panel) as reference (ref) is indicated.

[0042] FIG. 2 shows the result of the corrosion resistance test (according to ISO 9227) of an aluminium 2024 panel treated with a conventional passivation solution (see recipe in Example 1) and an inventive post-treatment solution (see recipe in Example 4) according to the protocol of Example 5. It can be seen in the pictures of FIG. 2A and FIG. 2B that the first corrosion pit appeared on the panel only after 312 hours.

[0043] FIG. 3 shows the paint adhesion properties of the coatings on an aluminium 2024 panel after having been treated with the conventional passivation solution (see recipe of Example 1), said conventional passivation solution and an inventive post-treatment solution (see recipe of Example 4) and an Alodine 1200 panel as reference. In this experiment, the treated panels were painted with a solvent-based polyurethane primer (PAC 33) and top-coat (PU 66-8H) (from PPG AEROSPACE). Ratings, per ASTM 3359, are based on a scale of 0 to 5, with 0 being the best rating.

[0044] FIG. 4 shows the result of the corrosion resistance test (according to ISO 9227) of an aluminium 2024 panel treated with a conventional passivation solution (see recipe in Example 1) and an inventive post-treatment solution (see recipe in Example 4) according to the protocol of Example 6. It can be seen that even after 648 hours of exposure to NSST, the visual aspect is good and no pits have emerged.

EXAMPLE 1PRODUCTION OF A CONVENTIONAL AND SPECIAL PASSIVATION SOLUTION

[0045] A conventional passivation solution is produced by mixing 100 ml of Lanthane 613.3 part A and 75 ml of part B (Coventya) with demineralized water to make up one liter of solution. The pH of said solution is adjusted to pH 4 (e.g. using 10% ammonia solution in water).

[0046] The special passivation solution is identical to the conventional passivation above with the exception that it comprises 4 g/L of a mixture of azoles. Specifically, the special passivation solution is produced by mixing 100 ml of Lanthane 613.3 part A and 75 ml of part B (Coventya) with 4 g/L of a mixture of azoles and demineralized water to make up one liter of solution. The pH of said solution is adjusted to pH 4 (e.g. using 10% ammonia solution in water).

EXAMPLE 2PRODUCTION OF A REFERENCE POST-TREATMENT SOLUTION

[0047] The reference post-treatment solution is produced by mixing 2 g of mercaptobenzothiazole, 4 g of triethanolamine and 1 g of Mowiol 4-88 with demineralized water to make up one liter of solution. Said solution is stirred until all compounds are dissolved. Then, the pH is adjusted to pH 10.5 (e.g. using 10% H.sub.2SO.sub.4 in water).

EXAMPLE 3PRODUCTION OF AN INVENTIVE POST-TREATMENT SOLUTION WITHOUT A WETTING AGENT

[0048] The inventive post-treatment solution without a wetting agent is produced by mixing 10 g/L (dry content) of an acrylic modified polymer, 4 g/L of a mixture of azoles (2-aryl-triazole and 2-aryl-alkyl-triazole) with demineralized water to make up one liter of solution.

[0049] The inventive post-treatment solution is stable for at least 10 weeks. On the contrary, the reference post-treatment solution (according to Example 2) shows precipitation even after 5 days i.e. is less stable.

EXAMPLE 4PRODUCTION OF AN INVENTIVE POST-TREATMENT SOLUTION COMPRISING WETTING AGENT

[0050] The inventive post-treatment solution comprising a wetting agent is produced by mixing 10 g/L (dry content) of an acrylic modified polymer, 4 g/L of a mixture of azoles (2-aryl-triazole and 2-aryl-alkyl-triazole) and 1.5 g/L of a wetting agent (siloxane based) with demineralized water to make up one liter of solution.

EXAMPLE 5METHOD OF PRODUCING A PROTECTIVE COATING OVER A Cr(III) CONVERSION LAYER AND FEATURES OF THE PRODUCED PROTECTIVE COATINGS

[0051] The method comprises the following steps: [0052] 1. Clean surface of aluminium, aluminium alloy, anodized aluminium or anodized aluminium alloy with soft alkaline cleaner (LUMIA CLEAN 101; 40 g/L) at 55 C. for 10 min; [0053] 2. Rinse surface two times with demineralised water; [0054] 3. Contact surface with Deoxidizing/Desmutting solution (LUMIA DEOX 411; 20 vol.-%) at room temperature (25 C.) for up to 10 min, preferably up to 1 min; [0055] 4. Rinse surface two times with demineralised water; [0056] 5. Passivate surface with passivation solution (conventional or special passivation solution; recipe see Example 1) at 40 C. for 5 min; [0057] 6. Rinse surface two times with demineralised water; [0058] 7. Contact surface with post-treatment solution (reference or inventive post-treatment solution; recipes see Examples 2 to 4) for 1 min.; [0059] 8. Dry surface at 50 C.

[0060] Features of the Produced Protective Coatings

[0061] I.) Glow Discharge Optical Emission Spectrometry (GDOES) of the Protective Coatings

[0062] Modified Cr(III) conversion coatings were produced with the method of Example 5 and the two different inventive post-treatment solutions mentioned in Examples 3 and 4.

[0063] The obtained modified coatings had the following properties:

TABLE-US-00001 thickness of coating coating comprising elements Example 3: ca. 70 nm 50 at.-% O, 40 at.-% C and 5 at.-% S; Example 4: ca. 80 nm 50 at.-% O, 40 at.-% C and 5 at.-% S.

[0064] Importantly, both inventive solutions produced a coating having a significant content of carbon and sulfur.

[0065] II.) Corrosion Resistance of the Protective Coatings

[0066] Cr(III) conversion coatings produced with the method of Example 5 were exposed to NSST (according to ISO 9227).

[0067] In the case that the substrate aluminium 2024 was only treated with the conventional passivation solution (for recipe see Example 1) i.e. was not treated with a post-treatment solution, first pits were appearing even after 96 hours. In other words, it turned out that the addition of a post-treatment solution is necessary to reach at least 168 hours until first pits are appearing. The obtained result is illustrated in FIG. 1 which contains a comparison of the number of pits after time for a treatment with the conventional passivation solution of Example 1 compared to a treatment of both the conventional passivation solution of Example 1 and the inventive post-treatment solution of Example 4.

[0068] In the case that the aluminium 2024 was treated with the conventional passivation solution (recipe see Example 1) and i) the first inventive post-treatment solution (recipe see Examples 3), or ii) the reference post-treatment solution (recipe see Example 2), the observed corrosion resistance was equal (pits appearing after approx. 216 hours; data not shown). However, FIG. 2 illustrates that in the case of a treatment with the second inventive post-treatment solution (i.e. the solution of Example 4), one first pit appeared only after 312 hours.

[0069] However, in the case that the aluminium 2024 was treated with the special passivation solution (recipe see Example 1) and the first inventive post-treatment solution (recipe see Examples 3), the second inventive post-treatment solution (recipe see Example 4) or the reference post-treatment solution (recipe see Example 2), the observed corrosion resistance was equal in all cases, but improved over the treatment with the conventional passivation solution (pits appearing only after approx. 264 hours; data not shown).

[0070] This result indicates that 2-aryl-triazole is effective in improving corrosion protection not only when present in the post-treatment solution, but also when present in the passivation solution.

[0071] II.) Aspect of the Protective Coatings

[0072] In the case that the conventional passivation solution (of Example 1) was used together with the reference post-treatment solution (of Example 2), the aspect of the protective coating was observed to be hazy.

[0073] On the contrary, in the case that the conventional passivation solution (of Example 1) was used together with an inventive post-treatment solution (of Example 3 or Example 4), the aspect of the protective coating was observed to be homogeneous.

[0074] IV.) Paint Adhesion Properties of the Protective Coatings

[0075] Aluminium 2024 panels were treated with passivation solution with or without post-treatment solution.

[0076] These panels were painted with solvent-based polyurethane primer (PAC 33) and top-coat (PU 66-8H) from PPG AEROSPACE.

[0077] Aluminum 2024 panels were prepared as usual with an immersion time in the TCP solution of about five minutes. Adhesion of primers to TCP coatings was evaluated against Alodine 1200, a chromate conversion coating, per MIL-DTL81706.

[0078] Ratings, per ASTM 3359, are based on a scale of 0 to 5, with 0 being the best rating. Results of these paint adhesion tests are shown in FIG. 3.

[0079] V.) Electrical Contact Resistance of the Protective Coatings

[0080] The treatment has to allow maintenance of low electrical contact resistance in a corrosive environment. Tests were performed according to MIL DTL 81706 and recorded values are:

TABLE-US-00002 Contact resistance before NSST after NSST Example 1: 5 m 2.3 m Example 4: 5 m 4.4 m Alodine 1200 19.3 m 28.5 m

[0081] Electrical resistivity is still below reference.

[0082] According to MIL DTL 81706, the electrical resistivity must be <5 m before Neutral Salt Spray Test and <10 m after Neutral Salt Spray Test. The treatment according to the invention enables to stay within the targeted values.

EXAMPLE 6FURTHER METHOD OF PRODUCING A PROTECTIVE COATING OVER A Cr(III) CONVERSION LAYER AND FEATURES OF THE PRODUCED PROTECTIVE COATINGS

[0083] The method comprises the following steps: [0084] 1. Clean surface of aluminium, aluminium alloy, anodized aluminium or anodized aluminium alloy with soft alkaline cleaner (LUMIA CLEAN 101; 40 g/L) at 55 C. for 10 min; [0085] 2. Rinse surface two times with demineralised water; [0086] 3. Contact surface with Deoxidizing/Desmutting solution (LUMIA DEOX 411; 20 vol.-%) at room temperature (25 C.) for up to 10 min, preferably up to 1 min; [0087] 4. Rinse surface two times with demineralised water; [0088] 5. Passivate surface with passivation solution (conventional or special passivation solution; recipe see Example 1) at 40 C. for 5 min; [0089] 6. Rinse surface two times with demineralised water; [0090] 7. Contact surface with post-treatment solution (inventive post-treatment solution; recipe see Example 4) for 1 min.; [0091] 8. Dry surface at 40 C.; [0092] 9. (Again) contact surface with post-treatment solution (inventive post-treatment solution; recipe see Example 4) for 1 min.; [0093] 10. Dry surface at 40 C.

[0094] Corrosion Resistance of the Protective Coatings

[0095] Cr(III) conversion coatings produced with the method of Example 6 were exposed to NSST (according to ISO 9227).

[0096] In the case that the aluminium 2024 was treated with the solution of Example 4 according to the protocol of Example 6, no pit appeared even after 648 hours of NSS exposure (see FIG. 4).

[0097] This result indicates that a twice treatment with the inventive post-treatment solution separated by a drying step very strongly improves corrosion protection.