Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Patent
1996-05-23
1997-12-30
Gorgos, Kathryn L.
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
204495, 204499, 204504, 204506, C25D 1320
Patent
active
057025819
DESCRIPTION:
BRIEF SUMMARY
This application is a National Stage Application of PCT/EP94/02872, filed Aug. 31, 1994, which published as WO 95/07319 on Mar. 16, 1995.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for coating metal substrates with a reduction of the process steps that are required, as well as the workpieces obtained thereby.
2. Description of the Prior Art
When outstanding corrosion protection is desired and good substrate adhesion of the lacquer coating produced by electrophoretic deposition is to be achieved the pre-treatment of metal substrates for a dip lacquer coating to be applied electrophoretically comprises a phosphate treatment and a passivating subsequent wash. The electro dip lacquer coating is then applied to this surface and stoved.
In series motor vehicle lacquering it has, for example, proved successful for the cleaned shells of galvanized or ungalvanized steel initially to be phosphated and then provided with a passivating subsequent wash before a so-called cathodic dip lacquer (CDL) is applied as a primer by cathodic deposition (see Glasurit-Handbuch der Lacke und Farben, p. 454 ff., 11th edition, 1984, Curt R. Vincentz Verlag Hanover). In this case the passivation step is a necessary component of the process.
In the last few years this basic process, which had been carried on in this way until today, has been constantly improved as regards the composition of phosphate treatment and passivating materials as well as the CDL materials. Phosphate treatment and passivating materials, for example, have been further developed as regards their technological properties and from ecological viewpoints, as Horst Gehmecker relates in JOT, Vol. 5, 1992, p. 42-46.
Alternative phosphate treatment processes such as iron phosphate treatment, zinc phosphate treatment, low-zinc phosphate treatment, tri-cation phosphate treatment, manganese-doped phosphate treatment, nickel-free phosphate treatment and nitrite-free phosphate treatment have become known, as the extensive patent literature demonstrates. Phosphate treatment solutions with a nickel ion content have proved particularly advantageous. Henkel markets commercial phosphate treatment products, for example, under the name Granodine.RTM., such are Granodine 950, a tri-cation system, Granodine 1990, a nitrite-free tri-cation system, or Granodine 2700, a nickel-free tri-cation system.
The search for alternatives to the original passivation solutions, which contain chromate and are still conventional today, which are more acceptable from an ecological and health point of view has met with success as the patent literature shows, for example. Examples are passivation solutions based on zirconium fluoride or organically based. Henkel, for example, markets passivation products under the name Deoxylyte.RTM., such as Deoxylyte 41, a chromate system, Deoxylyte 54 NC, a zirconium fluoride system or Deoxylyte 80, an organically based system.
Irrespective of the good properties regarding substrate adhesion and corrosion protection that can be achieved with the process described above, a disadvantage lies in the great deal of space required by the pre-treatment plants. Furthermore, when the various pre-treatment solutions are used a great deal of waste water is generated in the washing zones, and this requires complicated treatment.
A wide diversity of electro dip lacquers is known. Generally speaking they contain crosslinking catalysts, particularly in the form of heavy metal compounds. Lead or tin catalysts in particular have been used in practice.
Lead-free electro dip lacquers have also become known in more recent times, but they require improvement as regards their corrosion protection.
EP-A-138 193 describes the use of salts, specifically the acetates, preferably of divalent metals to improve the solubility of polymers. Bismuth is one of the metals mentioned. Improved lacquer film properties are not described.
SUMMARY OF THE INVENTION
The object of the invention is to provide a simplified process compared with the prior art fo
REFERENCES:
patent: 4673444 (1987-06-01), Saito et al.
patent: 4785068 (1988-11-01), Tominaga et al.
patent: 5066689 (1991-11-01), Patzschke et al.
patent: 5554700 (1996-09-01), Schipfer et al.
Hamacher Peter
Kerlin Klaus Gunter
Gorgos Kathryn L.
Herberts GmbH
Mayekar Kishor
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