Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming nonmetal coating
Patent
1995-03-28
1996-04-02
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming nonmetal coating
205177, 205188, C25D 1136
Patent
active
055037330
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a process for phosphating galvanized steel surfaces, preferably electrolytically galvanized or hot-dip-galvanized steel strip surfaces, by immersion or spray-immersion treatment thereof with acidic aqueous solutions which, in addition to zinc, phosphate and nitrate ions, contain ions of at least two other divalent metals, the workpieces simultaneously being cathodically treated with a direct current.
STATEMENT OF RELATED ART
It has been known to the expert for some considerable time that high proportions of heavy metal ions, more particularly nickel ions, in phosphate coatings can lead to particularly effective corrosion prevention, cf. for example WO-A-85/03089. However, it is also known in this connection that, to obtain high nickel contents in phosphate coatings, high concentrations of nickel must also be present in the phosphating solutions to be used. On the one hand, this increases process costs in view of the high price of nickel. On the other hand, relatively large quantities of toxic nickel compounds also have to be removed from the spent phosphating solutions because, in general, only about 2% of the nickel is incorporated in the phosphate coatings from the phosphating solutions.
Accordingly, efforts are being made for ecological and physiological reasons to eliminate the need for nickel, which is classified as toxicologically particularly hazardous, without incurring disadvantages in regard to corrosion prevention and paint adhesion. EP-A-459 541 proposes using phosphating solutions containing 1 to 30 mg/l Cu(II) in addition to 0.3 to 1.7 g/l zinc and 0.2 to 4.0 g/l manganese for this purpose.
The positive effect of copper on the formation of phosphate coatings has been known for some time in the prior art, cf. for example W. Rausch, Die Phosphatierung von Metallen Title in English: The Phosphating of Metals!, 2nd Edition (Eugen G. Leuze Verlag, 1988), pages 20, 56, 79 et seq. and 107. The copper ions may be added either to the phosphating bath itself or to a preceding activating bath, for example based on colloidal titanium polyphosphates. For example, EP-A-454 211 describes an activating bath containing titanium phosphate to which copper is added in quantities of 1 to 100 mg/l. However, a copper content of 1 to 100 mm/l can also be expected to have a favorable effect on titanium-free activating baths of the type described, for example, in EP-A-340 530.
In addition, the application of electric current in phosphating processes is known per se. Thus, a cathodic treatment, for example, results in acceleration of the phosphating process (cf. M. H. Abbas, Finishing, October 1984, pages 30-31). Corrosion-inhibiting coatings can be applied by deposition to galvanized steel surfaces by using acidic aqueous solutions based on aluminum phosphate and/or magnesium phosphate or polycondensed phosphoric acid and simultaneously applying cathodic currents (cf. JP-A-77/047 537, JP-A-75/161 429 and JP-A-89/219 193). JP-A-85/211 080 relates to a process for the production of corrosion-inhibiting layers on metal surfaces using zinc phosphating solutions with periodic application of a cathodic current. A corrosion-resistant protective layer is produced in this way, particularly along the edges of the metal surfaces to be treated. A similar process is described in EP-A-171 790. In this process, the metal surfaces are treated after conventional zinc phosphating with an acidic aqueous solution containing zinc, phosphate and chlorine ions, a direct current simultaneously being applied to the metal surfaces acting as anodes.
According to JP-A-87/260 073, phosphating coatings of high abrasion resistance can be produced on iron in acidic phosphating baths containing phosphoric acid, manganese and copper ions to which cathodic currents are applied. However, the phosphating of surface-finished material and the simultaneous use of zinc ions are not mentioned in this document. The phosphating of electrolytically galvanized or hot-dip-galvanized steel surfaces by this proces
REFERENCES:
patent: 4639295 (1987-01-01), Miyamoto et al.
patent: 4865653 (1989-09-01), Kramer
patent: 5112414 (1992-05-01), Brands et al.
patent: 5401381 (1995-03-01), Seidel et al.
"Die Phosphatierung von Metallen", Eugen G. Leuze Verlag, 2nd Edition 1988, pp. 20, 56, 79 et seq. and 107.
M. H. Abbas, Finishing, Oct. 1984, pp. 30-31.
Brands Karl-Dieter
Seidel Reinhard
Speckmann Horst-Dieter
Veldman Gerard
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
Leader William T.
Niebling John
Szoke Ernest G.
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