Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Patent
1992-02-26
1994-12-06
Beck, Shrive
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
427409, 524589, 524591, 528 76, 528 77, 528 81, B05D 136, C08G 1834, C08G 1842
Patent
active
053709101
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the production of multicoat protective and/or decorative coatings on substrate surfaces, to water-thinnable coating compositions based on polyurethane resins as film formers for the production of the coatings and to the use of these water-thinnable coating compositions for the production of multicoat protective and/or decorative coatings on substrate surfaces.
In the field of automotive finishing in particular, but also in other areas where coatings with a good decorative effect and at the same time with anticorrosive characteristics are desirable, it is known practice to coat substrates with several coatings superimposed on one another.
Multicoat coatings are preferably applied by the so-called basecoat-clearcoat i.e. process, a pigmented basecoat paint is first applied which, after a brief flash-off period, is coated by a clearcoat paint without a baking stage (wet-on-wet process). The basecoat and the clearcoat are subsequently baked together.
The basecoat-clearcoat process has gained great importance especially in automotive metallic finishes.
Attempts have been made for economic and ecological reasons to use aqueous basecoat compositions for the production of multicoat coatings.
The coating compositions for the production of basecoats for multicoat automotive coatings must be capable of being processed by the expedient wet-on-wet process, customary today, i.e. they must be capable, after as short preliminary drying as possible, of being coated by a (transparent) topcoat without exhibiting any effects due to solvent action of one coat on the other.
In addition, other problems must be solved in the development of coating compositions for basecoats for metallic finishes. The metallic effect depends decisively on the orientation of the metallic pigment particles in the paint film. A basecoat for metallic finishes, capable of being processed by the wet-on-wet process, must therefore produce paint films in which the metallic pigments are present in a suitable spatial orientation after having been applied and in which this orientation becomes set so rapidly that it cannot be disturbed in the course of the further painting process.
In the development of water-thinnable systems which would meet the above requirements, problems have arisen which are due to the special physical properties of water and difficult to solve, and only a small number of water-thinnable paint systems, which can be used in the above sense, are known so far.
Thus, for example, DE 3,545,618 discloses according to the preamble of the main claim processes as well as aqueous coating compositions for the production of basecoats for multicoat coatings. The process and the coating composition, however, are in need of improvement in respect both of the stability of the system of coatings in a condensed water test under constant conditions of temperature and humidity according to DIN 50017 (October 1982 edition) and of the metallic effect attainable after the basecoat compositions have been stored for several weeks (known in its abbreviated form as effect stability).
EP-A-256,540 likewise discloses a wet-on-wet process for multicoat coating. The basecoat paints used therein contain as film former a mixture of (1) 90 to 40% by weight of a polymeric resin containing hydroxyl groups and (2) 10 to 60% by weight of a polyurethane dispersion, the sum of the components (1) and (2) being always 100% by weight. However, the polyurethane dispersions used containing urea groups give rise to coating compositions which dry too rapidly and are therefore unsuitable for any practical application especially in production line painting processes, since the said coating compositions adhere so well to the equipment by means of which they are applied that they can only be removed with considerable difficulties. This makes it impossible, especially in automotive production line painting, to make frequent and rapid changes of the applied paint system (for example when changing color).
Furthermore, the coating compositions accordin
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Dobbelstein, deceased Arnold
Hille Hans-Dieter
Muller Horst
Wieditz Stefan C.
BASF Lacke & Farben AG
Beck Shrive
Dudash Diana
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