Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly single metal or alloy coating on...
Patent
1993-04-29
1995-04-25
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly single metal or alloy coating on...
205173, 205253, 205303, 205324, C25D 332, C25D 1104
Patent
active
054095921
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a new electrolyte additive for a sulfuric acid coloring bath containing tin(II) for the alternating current coloring of anodized aluminum surfaces, which consists of a synergistic mixture of at least one antioxidant corresponding to one of general formulae I to IV and at least one throwing power improver corresponding to general formula V, and to a process for the alternating-current coloring of anodized aluminum surfaces using the electrolyte additive according to the invention.
STATEMENT OF RELATED ART
It is known that, on account of its base character, aluminum becomes covered with a natural oxide coating generally below 0.1 .mu.m in thickness (Wernick, Pinner, Zurbrugg, Weiner, Die Oberflachenbehandlung von Aluminum (The Surface Treatment of Aluminum), 2nd Edition, (Eugen Leuze Verlag, Saulgau/Wurtt., 1977).
Considerably thicker oxide coatings can be obtained by electrolytic oxidation of aluminum. This process is known as anodizing. Sulfuric acid, chromic acid or phosphoric acid is preferably used as the electrolyte. Organic acids, such as for example oxalic acid, maleic acid, phthalic acid, salicylic acid, sulfosalicylic acid, sulfophthalic acid, tartaric acid or citric acid, are also used in some processes.
However, sulfuric acid is the most commonly used electrolyte. Depending on the anodizing conditions, layer thicknesses of up to 150 .mu.m can be obtained in this process. However, layer thicknesses of 20 to 25 .mu.m are sufficient for external applications, such as for example facade facings or window frames.
The anodizing process is generally carried out in 10 to 20% sulfuric acid with a current density of 1.5 A/dm.sup.2, at a temperature of 18.degree. to 22.degree. C. and over a period of 15 to 60 minutes, depending on the required layer thickness and the particular application.
The oxide coatings thus produced have a high absorption capacity for a number of organic and inorganic substances or dyes.
Electrolytic coloring processes, in which anodized aluminum is colored by treatment with alternating current in heavy metal salt solutions, have been known since the middle of the thirties. The heavy metals used are, above all, elements of the first transition series, such as Cr, Mn, Fe, Co, Ni, Cu and, in particular, Sn. The heavy metal salts are generally sulfates, pH being adjusted to a value of 0.1 to 2.0 with sulfuric acid. The coloring process is carried out at a voltage of around 10 to 25 V and the resulting current density. The counter-electrode may either consist of graphite or stainless steel or of the same material which is dissolved in the electrolyte.
In this process, the heavy metal pigment is deposited in the pores of the anodic oxide coating in the half cycle of the alternating current in which aluminum is the cathode, the aluminum oxide coating being further thickened by anodic oxidation in the second half cycle. The heavy metal is deposited at the bottom of the pores and thus colors the oxide coating.
However, one of the problems encountered where coloring is carried out in tin electrolytes is that the tin readily oxidizes, so that basic tin(IV) oxide hydrates (stannic acid) are rapidly precipitated during the application and, in some cases, even during the storage of the Sn solutions. It is known that aqueous tin(II) sulfate solutions are oxidized to tin(IV) compounds simply by exposure to atmospheric oxygen or by reaction at the electrodes when current is applied. This is highly undesirable in the coloring of anodized aluminum in tin electrolytes because, on the one hand, it disrupts the process sequence (frequent renewal or topping up of the solutions rendered unusable by the formation of precipitates) and, on the other hand, leads to considerable extra costs because of the tin(IV) compounds which cannot be used for coloring. Accordingly, various processes have been developed, differing in particular in the means used to stabilize the generally sulfuric acid tin(II) sulfate solutions for the electrolytic coloring of aluminum.
P
REFERENCES:
patent: 4042468 (1977-08-01), Hasegawa et al.
patent: 5064512 (1991-11-01), Brodalla et al.
S. A. Pozzoli, F. Tegiacchi; Korros, Korrosionsschutz Alum., (Stability of the Bivalent Tin Solutions Used for the Electrolytic Coloring of Anodized Aluminum), (no month) 1976, pp. 139-145.
Lindener Juergen
Meyer Loert D.
Sander Volker
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
Niebling John
Szoke Ernest G.
Wisdom, Jr. Norvell E.
LandOfFree
Electrolyte additive for a colorant bath for coloring aluminum a does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrolyte additive for a colorant bath for coloring aluminum a, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrolyte additive for a colorant bath for coloring aluminum a will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1565576