Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1993-09-24
1995-01-10
Niebling, John
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
2041814, 523415, 523417, 524901, C25D 1304
Patent
active
053804120
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for coating electric ally conducting substrates, in which process
(1) the substrate is immersed in an aqueous electrocoating bath which contains a cationic amine-modified epoxy resin obtainable by reacting containing an alcoholic OH group, a phenolic OH group or an SH group, and preferably 4:1 to 1.5:1 and the positive charges being introduced by protonization of the reaction product and/or by use of amine salts as the component (C);
(2) the substrate is connected as cathode,
(3) a film is deposited on the substrate by the action of direct current,
(4) the substrate is removed from the electrocoating bath and
(5) the deposited paint film is baked.
The invention also relates to substrates coated by the process according to the invention and to the electrocoating baths employed in the process according to the invention.
The cathodic electrocoating process described above is a painting process frequently used primarily for priming, in particular for priming automotive bodies.
A process according to the preamble of patent claim 1 is known from DE-OS 3,518,732, DE-OS 3,409,188 and DE-OS 3,518,770.
Surface defects (particularly craters), well-known to a person skilled in the art, disadvantageously occur in the processes described in DE-OS 3,409,188, DE-OS 3,518,732. and DE-OS 3,518,770.
The object forming the basis of the present invention is to make available a novel process according to the preamble of patent claim 1, using which it is possible to produce paint films which, compared with paint films of prior art, exhibit fewer and/or more faintly pronounced surface defects and do not give rise to defects due to adhesion failure in overcoated paint films.
The object is achieved according to the invention by a process according to the preamble of patent claim 1, wherein the electrocoating bath contains at least 7.5% by weight of a polyoxyalkylenepolyamine or a mixture consisting of several polyoxyalkylenepolyamines of different chemical structures, the percentage by weight referring to the total amount of binders contained in the electrocoating bath.
The advantages achieved by the invention are essentially to be found in the fact that it is possible, using the process according to the invention, to obtain paint films which, compared with paint films of prior art, exhibit fewer and/or more faintly pronounced surface defects and do not give rise to defects due to adhesion failure in overcoated paint films, especially in overcoated paint films containing alkyd resins as binders.
Further important advantages achieved by the process according to the invention lie in the fact that, compared with prior art, the paint films obtained by the process according to the invention possess greater film thicknesses and greater flexibility.
U.S. Pat. No. 3,975,250 discloses cationic reactive plasticizers, suitable for use in electrocoating baths, which are prepared by the reaction of partly blocked polyisocyanates with polyoxypropylenediamines. However, an average person skilled in the art, faced with the object forming the basis of the present invention, is unable to infer from U.S. Pat. No. 3,975,250 any information for achieving this object.
U.S. Pat. No. 4,423,166 discloses an electrocoating process, wherein the electrocoating bath contains as anticratering agent an aduct of polyoxyalkylenepolyamine and a polyepoxide. However, the process disclosed in U.S. Pat. No. 4,423,166 does not use electrocoating baths according to the preamble of patent claim 1.
If, however, the anticratering agents disclosed in U.S. Pat. No. 4,423,166 are employed in a process according to the preamble of patent claim 1, then it is true that the tendency for surface defect formation is reduced, but instead problems due to adhesion failure occur in the overcoated paint films. Particularly serious problems occur in overcoated paint films containing alkyd resins as binders.
The advantages achieved by the present invention are the more surprising, since electrocoating baths are described in U.S. Pat. No. 4,423,166, colum
REFERENCES:
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patent: 3975250 (1976-08-01), Marchetti et al.
patent: 4423166 (1983-12-01), Moriarity et al.
patent: 4468307 (1984-08-01), Wismer et al.
patent: 4605690 (1986-08-01), Debroy et al.
patent: 4615779 (1986-10-01), McCollum et al.
patent: 4707232 (1987-11-01), Batzill et al.
patent: 4944855 (1990-07-01), Schon et al.
PCT WO87/05922, published on Oct. 8, 1987 and issued to Schon et al.
Jouck Walter
Ott Gunther
Reiter Udo
Ruhl Dieter
Santure David J.
BASF Lacke+Farben AG
Mayekar Kishor
Niebling John
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