Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Treating electrolytic or nonelectrolytic coating after it is...
Patent
1993-01-11
1994-08-16
Green, Anthony
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Treating electrolytic or nonelectrolytic coating after it is...
205316, 205333, 106 1405, 106 1421, 106490, C09D 544, C09D 508
Patent
active
053384342
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the coating of electrically conductive substrates, in which electrocoating paint,
The invention also relates to a cathodically depositable aqueous electrocoating paint.
The cathodic electrocoating painting process described above is known (cf. for example DE-A-3,518,732, DE-A-3,518,770, EP-A-4,090, EP-A-12,463 and EP-A-262,069) and is employed in particular for the priming of automobile bodies.
Very high-quality finishes can be obtained by the cathodic electrocoating process, especially by using electrocoating paints containing cationic, amine-modified epoxy resins as binders.
The electrocoating paints under discussion contain lead pigments to increase their anticorrosive effect. These pigments are toxicologically and ecologically not unobjectionable. A declared aim of paint manufacturers is to replace lead anticorrosive pigments with lead-free anticorrosive pigments. Although many lead-free anticorrosive pigments are known, this aim has so far not been achieved. The reason for this lies in the fact that replacement of lead anticorrosive pigments always results in impairment of the anticorrosive effect and/or the flexibility in bending and/or the adhesion and/or the impact resilience of the resultant finishes and/or the flow-out characteristics and/or the throwing power of the electrocoating paints. Even the lead-free anticorrosive pigments disclosed in DE-A-3,532,806, based on zinc silicate modified with B.sub.2 O.sub.3 and/or WO.sub.3 and/or MoO.sub.3 and/or SnO.sub.2 are no exception, although they are also recommended for use in electrocoating paints.
Many attempts have been made to compensate for the impairment of the paint characteristics arising when lead anticorrosive pigments are replaced with lead-free anticorrosive pigments by modifying the chemical structure of the principal binders and/or of the crosslinking agent and/or of the grinding resin and/or by varying the amounts of principal binder and/or of crosslinking agent and/or of grinding resin used and/or by varying the type and amount of the pigments and/or fillers used and/or by adding special additives. These attempts have so far produced only unsatisfactory results.
The object of the present invention is an improvement of the process described above for coating electrically conductive substrates. The object of the present invention is especially the provision of electrocoating paints which are suitable for the above process and in which lead anticorrosive pigments have been completely or at least partially replaced by lead-free anticorrosive pigments, the drawbacks described above occurring only to a reduced extent, if at all.
Surprisingly, this object is achieved by a process as classified in the preamble of claim 1, in which the aqueous electrocoating paint contains 2 to 10, preferably 4 to 6%, by weight of an anticorrosive pigment based on zinc silicate in combination with 1 to 15, preferably 2 to 4%, by weight of a very fine quartz powder or cristobalite powder coated with epoxysilane or aminosilane, the percentages by weight being based on the total solids content of the electrocoating paint and the anticorrosive pigment being preparable by fusing together 35 to 65% by weight of ZnO, 15 to 35% by weight of SiO.sub.2 and 0 to 20% by weight of B.sub.2 O.sub.3 and/or 0 to 20% by weight of WO.sub.3 and/or 0 to 20% by weight of MoO.sub.3 and/or 0 to 20% by weight of SnO.sub.2, the components being fused together using at least one of the cited oxides besides ZnO and SiO.sub.2 in such a manner that the percentages by weight always total 100.
Surprisingly, when the electrocoating paints according to the invention are used, finishes are obtained which are equivalent in quality to the finishes obtained with electrocoating paints containing lead pigments.
The use of very fine quartz powder or wollastonite powder with surfaces treated with epoxysilane as anticorrosive fillers in non-aqueous paints is described in DE-A-3,325,064. DE-A-3,325,064 provides no indication that the specific combination according
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Arlt Klaus
Heilmann Ulrich
Heimann Ulrich
Hoffmann Udo
Ruhl Dieter
BASF Lacke & Farben Aktiengesellschaft
Green Anthony
Sabourin Anne G.
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