Process for coating electrically conductive substrates, aqueous

Details Process for coating electrically conductive substrates, aqueous Process for coating electrically conductive substrates, aqueous

1991-12-11

1993-11-16

Marquis, Melvyn I.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

523417, 2041814, 2041817, C08L 6302

Patent

active

052624650

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for coating electrically conductive substates, in which which contains at least one cationic, amine-modified epoxy resin as binder,
The invention also relates to an aqueous coating composition, which contains a cationic, amine-modified epoxy resin as binder, a process for the preparation of a cationic, amine-modified epoxy resin and a cationic, amine-modified epoxy resin prepared according to this process.
The process described above is known (cf. for example, DE-OS 3,518,732, DE-OS 3,518,770 and U.S. Pat. No. 3,984,299) and is used particularly for priming automobile bodies. The coatings obtainable by the process described above need to be improved in respect of layer thickness, flow properties, stone-chip resistance, flexibility, adhesion characteristics and corrosion protection on non-pretreated sheet metal.
In the process described above it is also desirable to use electro-dipcoating compositions with a very low organic solvent content.
The underlying object of the present invention comprises the provision of a new process in accordance with the preamble of patent claim 1, with which coatings can be obtained which do not have the disadvantages of the prior art described above or have then disadvantages to a lesser extent.
This object is surprisingly achieved by a process in accordance with the preamble of patent claim 1, in which the electro-dipcoating composition contains a cationic, amine-modified epoxy resin which is obtainable by reacting and particularly preferentially 2.0 epoxy groups per molecule, or a mixture of such compounds, and weight of 400 to 5,000, preferably 600 to 2,000, or a mixture of such polyether- and/or polyester-polyols, towards isocyanate groups and at least one ketimine group in the molecule, or a mixture of such compounds, with one another, and/or at least one ketimine group in component (C) to a primary amino group by hydrolysis, to 80% of the epoxy groups of component (A) are reacted with component (B) and the remaining epoxy groups are reacted with component (C) and/or (D) and --if still necessary--is at least partially protonating the reaction product thus obtained.
The coatings prepared in accordance with the process according to the invention are distinguished by large layer thicknesses, good flow properties, high stone-chip resistance, high flexibility, good adhesion characteristics and good corrosion protection on non-pretreated sheet metal. A further important advantage of the process according to the invention is that the electro-dipcoating compositions used, which, in comparison to the prior art, have a very low organic solvent content, produce coatings with the good properties described above.
The cationic, amine-modified epoxy resins used according to the invention are obtainable by reacting the components (A) and (B) and (C) and/or (D) with one another in a relative proportion such that 20 to 90, preferably 60 to 80% of the epoxy groups of component (A) are reacted with component (B) and the remaining epoxy groups are reacted with component (C) and/or (D) and the reaction product thus obtained is--if necessary--at least partially protonated. The reaction of the components (A), (B), (C) and/or (D) is carried out in an organic solvent (for example xylene, butyl glycol, butanol and the like.) or in a mixture of organic solvents, at temperatures of from 20.degree. to 160.degree. C., preferably 80.degree. to 130.degree. C. If a substance containing ketimine groups is used as component (C) and/or (D), it is then expedient to carry out the reaction in the presence of water and/or a Br nsted acid. It is preferred to react the components (A) and (B) in a first step to give an intermediate containing epoxy groups, and then to react this intermediate with component (C) and/or (D) in a second step. In principle it is also possible--but less preferred--to prepare an intermediate containing epoxy groups from components (A) and/or (C) and/or (D), which intermediate is further reacted with component (B) in a second step. With this procedure su

REFERENCES:
patent: 3947339 (1976-03-01), Jerabek et al.
patent: 4824927 (1989-04-01), Dobbelstein et al.
patent: 4956402 (1990-09-01), Perner et al.

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