Process for the production of multi-layer coatings

Abstract

A process for the production of multi-layer coatings comprising the successive steps: 1) applying an 8 to 20 μm thick coating layer from an aqueous coating composition A onto a substrate provided with an EDC primer, 2) applying a 5 to 15 μm thick base coat layer from an aqueous coating composition B onto the previously applied coating layer, 3) applying a clear coat layer onto the base coat layer, 4) jointly curing the three coating layers, wherein coating compositions A and B being different from each other and wherein the coating composition A contains at least one metal platelet pigment having a thickness from 10 to 100 nm in a proportion corresponding to a pigment/resin solids ratio by weight from 0.06:1 to 0.2:1.

Description

BACKGROUND OF THE INVENTION [0001] The invention relates to a process for the production of multi-layer coatings. DESCRIPTION OF THE PRIOR ART [0002] Automotive coatings consist, as a rule, of a separately baked electrodeposition coating (EDC) primer, a separately baked primer surfacer layer (filler layer) applied thereto and 20 to 35 μm thick in general and a top coat applied thereto comprising a wet-on-wet applied color- and / or special effect-imparting base coat layer, 10 to 25 μm thick in general, and a protective, gloss-imparting clear coat layer. The total primer surfacer plus base coat layer thickness is generally 30 to 60 μm. [0003] There is the desire to decrease total primer surfacer plus base coat layer thickness and to avoid the application of a primer surfacer layer and the separate baking thereof. [0004] Processes are known from WO 97 / 47401 and U.S. Pat. No. 5,976,343 for the production of decorative multi-layer coatings, which processes allow for the elimination of the...

AI Technical Summary

Problems solved by technology

A weakness of the processes known from WO 97 / 47401 and U.S. Pat. No. 5,976,343 is that it is not readily possible to produce multi-layer coatings in certain color shades (“problematic color shades”).

The color shades which are problematic with regard to the production of primer surfacer-free multi-layer coatings are those which, while (like unproblematic color shades) providing a coating which appears to an observer to be opaque, permit an inadmissibly large amount of UV light to penetrate through the multi-layer structure consisting of clear coat, unmodified water-borne base coat and modified water-borne base coat to the surface of the EDC primer and cause long term damage to the EDC layer.

Such problematic color shades are to be found both among single (plain) color shades and special effect color shades.

The possible undesired long-term consequences of an inadmissible level of UV light penetration to the EDC layer are chalking of the EDC layer and delamination of the multi-layer coating over the service life of the coated substrates.

However, UV absorbers cannot be used to a very great extent in the base coat layers and / or the clear coat layer because of the migration tendency of the UV absorbers and because of the gradual degradation of the UV absorbers, as well as for cost reasons.

This inevitably restricts the EDC composition, such that concessions may have to be made in relation to other technological properties, such as, for example, corrosion protection.