Process for coating phosphated metal substrates

Details Process for coating phosphated metal substrates Process for coating phosphated metal substrates

1997-02-26

1998-06-30

Gorgos, Kathryn L.

Coating processes

With pretreatment of the base

Metal base

427330, 204499, 205210, 205317, 205318, 148286, 148287, B05D 300, C25D 534, C25D 902, C23C 810

Patent

active

057730903

DESCRIPTION:

BRIEF SUMMARY
This is a national stage application of PCT/EP95/01957 filed May 23, 1995.
1. Field of the Invention
This invention relates to a process for coating phosphated metal substrates with organic coatings, in particular electrocoated lacquer coatings.
2. Description of the Related Art
Metallic substrates, for example made from aluminium, but in particular from galvanised or ungalvanised steel, are pretreated for lacquer coating, in particular for an electrophoretically applied lacquer coating, if good anti-corrosion properties are desired and good substrate adhesion of the lacquer layer formed by electrophoretic deposition is to be achieved in a pretreatment process comprising phosphating and a passivating rinsing. The electrocoated lacquer coating is then applied onto this surface and stoved.
It has, for example, become standard practice in automotive original lacquer coating for the cleaned bare bodywork made from galvanised or ungalvanised steel first to be phosphated and then post-treated with a passivating rinsing before a so-called cathodic electrocoating is applied by cathodic deposition as a priming layer (c.f. Glasurit-Handbuch der Lacke und Farben, pages 454 et seq., 11th edition, 1984, Curt R. Vincentz Verlag, Hannover). The passivation stage is a necessary part of this process.
In recent years, this basic process which has hitherto been performed in this manner has undergone constant improvement with regard to the composition of the phosphating and passivating materials and of the cathodic electrocoating material. For example, phosphating and passivating materials have been further developed both with regard to their technical characteristics and with regard to their environmental properties, as described by Horst Gehmecker in JOT, issue 5, 1992, pages 42 to 46.
Phosphating variants which have become known are, for example, iron phosphating, zinc phosphating, low-zinc phosphating, tricationic phosphating, manganese-doped phosphating, nickel-free phosphating and nitrite-free phosphating, as is demonstrated by the comprehensive patent literature. Phosphating solutions containing toxic nickel ions have proved particularly technically advantageous. Commercial phosphating products are sold, for example, by Henkel under the names Granodine.RTM., for example Granodine 950 as a tricationic system, Granodine 1990 as a nitrite-free tricationic system or Granodine 2700 as a nickel-free tricationic system.
The search for alternatives which are less questionable on environmental and health grounds to the original and still widely used passivating solutions containing chromate has met with success, as is substantiated by the patent literature. Examples of such alternatives are passivating solutions based on zirconium fluoride or organic compounds. Henkel, for example, thus sells passivating products under the trade name Deoxylyte.RTM., for example, Deoxylyte 41 as a chromate system, Deoxylyte 54 NC as a zirconium fluoride system or Deoxylyte 80 as an organically-based system. Such passivating solutions are distinguished by a complicated composition.
Polym. Mater. Sci. Eng., volume 58, 1988 (pages 176 to 177) describes a process for post-treating phosphate layers before application of an organic coating with an aqueous solution containing tin ions. U.S. Pat. No. 4,828,615 describes the treatment of phosphated surfaces, before application of coating compositions, with an aqueous solution containing pentavalent vanadium compounds. DE-A-23 24 342 relates to an aqueous rinsing agent containing rare earth metals with which inter alia phosphated surfaces are treated before application of a coating of paint. JP-A-58 130 282 describes the treatment of phosphated surfaces with aqueous Fe, Zn, Ni, Mo, Co, W, Mg, Mn or Si solutions before the surfaces receive a coating.


SUMMARY OF THE INVENTION

An object of the present invention is to provide a coating process for phosphated metal substrates which increases corrosion protection beyond previously achieved levels. It should preferably be possible to perform the coating proce

REFERENCES:
patent: 4828615 (1989-05-01), Cape
patent: 5061315 (1991-10-01), Collier et al.
patent: 5385655 (1995-01-01), Brent et al.
58-130282, "Pretreatment of Metal for Coating", Shin Nippon Seitetsu K.K., C23C22/83, abst. Aug. 3,1983.
153793e, "Laboratory Studies of a New Pretreatment Method", p. 275, Oct. 1988, No. 18, Columbus, OH (abst).
Glasurit-Handbuch, 1984, Translation of the yellow marked passages on p. 456. No month available.
Patent Abstracts of Japan 007 (242), Oct. 27, 1983 & JP, A,130282 (Shin Nippon Seitetsu KK).
Chemical Abstracts, 109 (18) 153793e (Oct. 31, 1988) Ledheiser, "Laboratory Studies of a New Pretreatment Method".
Chemical Abstracts, 97 (26) 220959n (Dec. 27, 1982) Belyi, "Additional Treatment of porous phosphate coatings"& SU-A-914, 652.
Chemical Abstracts 107 (14) 135294x (Oct. 5, 1987) & JP-A-62 032113 (Shikoku Chem. Corp.).

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