Process for coating electrically conductive substrates, an aqueo

Details Process for coating electrically conductive substrates, an aqueo Process for coating electrically conductive substrates, an aqueo

1992-01-24

1997-12-02

Seidleck, James J.

Chemistry: electrical and wave energy

Processes and products

Electrophoresis or electro-osmosis processes and electrolyte...

204509, 523414, 525440, 528 83, 528 85, C09D 544

Patent

active

056932057

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for coating electrically conductive substrates in which electro-dipping primer,
The invention also relates to an aqueous coating composition, a process for the preparation of an adduct containing urethane groups and an adduct containing urethane groups.
The cathodic electro-dipping process described above is known (compare, for example, DE-OS-3,518,732, DE-OS-3,518,770, EP-A-4,090, EP-A-12,463 and EP-A-262,069) and is used, in particular, for priming automobile bodies.
Coatings of outstanding quality can be obtained with the aid of the cathodic electro-dipping process--especially if electro-dipping primers containing cationic amine-modified epoxy resins as binders are used.
EP-A-262,069 discloses that the flexibility, impact resilience and stone-chip resistance of the resulting coatings can be improved by addition of adducts containing urethane groups to electro-dipping primers. However, the addition of the adducts containing urethane groups which are disclosed in EP-A-262,069 adversely lead to a reduction in the solvent resistance of the stoved films and to a reduction in the storage stability of the electro-dipping primers. The addition of the adducts containing urethane groups which are disclosed in EP-A-262,069 furthermore also has an adverse effect on the anticorrosion properties of the resulting coatings.
The object on which the present invention is based consists of providing a novel process according to the precharacterizing clause of patent claim 1, with which coatings which do not have the disadvantages of the prior art described above, or have them to a decreased extent, can be obtained.
This object is achieved, surprisingly, by a process according to the precharacterizing clause of patent claim 1, in which the aqueous electro-dipping primer contains an at least partly protonated adduct containing urethane groups which is obtainable by reacting with one another weight of 400 to 5000, preferably 600 to 2000, or a mixture of such polyether- and/or polyester-polyols, group in the molecule or a mixture of such compounds, hydrolysis of the ketimine groups.
In comparison with the coatings produced according to EP-A-262,069, the coatings produced by the process according to the invention are superior in respect of solvent resistance, anticorrosion properties, flexibility, impact resilience, stone-chip resistance and adhesion to the substrate. Electro-dipping primers which contain the adducts containing urethane groups employed according to the invention moreover exhibit a better storage stability than electro-dipping primers which contain the adducts containing urethane groups which are disclosed in EP-A-262,069.
The electro-dipping primers employed according to the invention usually contain at least one synthetic resin which can be deposited cathodically, if appropriate at least one crosslinking agent and pigments, fillers, at least one grinding resin and other additives which are generally well known, such as foam suppressants, flow control auxiliaries and the like.
The electro-dipping primers employed according to the invention can in principle contain all the externally crosslinking or self-crosslinking synthetic resins which can be deposited cathodically and are suitable for the preparation of electro-dipping primers. The electro-dipping primers employed according to the invention can also contain mixtures of different synthetic resins which can be deposited cathodically.
However, the electro-dipping primers which contain cationic amine-modified epoxy resins as the synthetic resins which can be deposited cathodically are preferred. Both self-crosslinking and externally cross-linking cationic. amine-modified epoxy resins are known. Externally crosslinking cationic amine-modified epoxy resins are preferably employed.
Cationic amine-modified epoxy resins are understood as cationic reaction products of
Polyepoxides are understood as compounds which contain two or more epoxide groups in the molecule.
Particularly preferred (a) components are compounds which can be pre

REFERENCES:
patent: 5015672 (1991-05-01), Perner et al.
Lee & Neville, Handbook of Epoxy Resins (1967), pp. 7-25.

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