Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming multiple superposed electrolytic coatings
Patent
1993-10-06
1995-03-28
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming multiple superposed electrolytic coatings
204188, 204199, 204318, 205318, C25D 1136
Patent
active
054013810
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a process for phosphating metal surfaces, preferably electrolytically galvanized or hot-dip-galvanized steel strip surfaces, by the dip or spray-dip treatment thereof with acidic aqueous solutions which, in addition to zinc, phosphate and nitrate ions, contain ions of at least one other divalent metal, the workpieces being cathodically treated with a direct current at the same time.
STATEMENT OF THE RELATED ART
The use of electrical current in phosphating processes is known per se. Thus, a cathodic treatment, for example, accelerates the phosphating process (see M. H. Abbas, Finishing, October 1984, pages 3-31). Anti-corrosion layers can be deposited on galvanized steel surfaces by means of acidic aqueous solutions based on aluminum phosphate and/or magnesium phosphate or polycondensed phosphoric acid with simultaneous application of cathodic currents (cf. JP-A-77/047 537, JP-A-75/161 429 and JP-A-89/219 193). In addition, phosphate coatings of high abrasion resistance can be formed on metal surfaces using acidic phosphating baths containing phosphoric acid, manganese and copper ions with simultaneous application of cathodic currents (JP-A-87/260 073). JP-A-85/211 080 relates to a process for producing anti-corrosion layers on metal surfaces using zinc phosphating solutions with periodic application of a cathodic current. In this process, a corrosion-resistant protective layer is also produced in particular at the edges of the metal surfaces to be treated. A similar process is described in EP-A-0 171 790. In this process, the metal surfaces, which have already been zinc-phosphated in the usual way, are treated with an acidic aqueous solution containing zinc, phosphate and chlorine ions, a direct current being simultaneously applied to the metal surfaces acting as anodes.
On the other hand, it has long been known to the expert that high nickel contents in phosphate coatings lead to particularly good protection against corrosion. However, it is also known in this connection that, to obtain high nickel contents in the phosphate coatings, the phosphating solutions to be used are also required to have high nickel contents. On the one hand, this leads to higher process costs because of the high price of nickel. On the other hand, relatively large quantities of toxic nickel compounds have to be removed from the spent phosphating solutions because, in general, only about 2% of the nickel from the phosphating solutions is incorporated in the phosphate coatings. Thus, a high nickel zinc phosphating process is known from WO-A-85/03 089 for example. In this process, extremely high concentrations of nickel are used for phosphating. It is generally pointed out that, in principle, the nickel may be partly replaced by a number of monovalent or divalent cations selected, for example, from cobalt, manganese and magnesium. It is also pointed out that the nickel content of the solution to be used must be at least 1.0 g/l. The ratio to be established between a low zinc content and a high nickel content is a key part of the technical teaching.
DESCRIPTION OF THE INVENTION
By contrast, the problem addressed by the present invention was to provide a process for phosphating metal surfaces in which the incorporation rate of nickel and/or cobalt in the phosphate coatings formed could be significantly increased although only comparatively low concentrations of nickel and/or cobalt cations are present in the phosphating baths used.
SUMMARY OF THE INVENTION
Accordingly, the present invention relates to a process for phosphating metal surfaces, preferably electrolytically galvanized or hot-dip-galvanized steel strip surfaces, by the dip or spray-dip treatment thereof with acidic aqueous solutions which, in addition to zinc, phosphate and nitrate ions, also contain ions of at least one other divalent metal, characterized in that: 80.degree. C., direct current having a density in the range from 0.01 to 100 mA/cm.sup.2.
It has surprisingly been found that the rate of incorporation
REFERENCES:
patent: 3449229 (1969-06-01), Freeman et al.
patent: 4639295 (1987-01-01), Miyamoto et al.
patent: 4865653 (1989-09-01), Kramer
patent: 4874480 (1989-10-01), Sonoda et al.
M. H. Abbas, Finishing, Oct. 1984, pp. 30-31.
Brands Karl-Dieter
Mady Raschad
Seidel Reinhard
Speckmann Horst-Dieter
Veldman Gerard
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
Leader William T.
Niebling John
Szoke Ernest G.
LandOfFree
Process for phosphating metallic surfaces does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for phosphating metallic surfaces, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for phosphating metallic surfaces will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2247989