Citation
Bean, J. (2002), "Who's next for automotive powder clearcoats?", Pigment & Resin Technology, Vol. 31 No. 5. https://doi.org/10.1108/prt.2002.12931eaa.001
Publisher
:Emerald Group Publishing Limited
Copyright © 2002, MCB UP Limited
Who's next for automotive powder clearcoats?
Who's next for automotive powder clearcoats?
To our knowledge there are only two major car manufacturers in Europe who are using powder clearcoats on a large scale. With the advantages offered, particularly in meeting the ever more stringent regulations on solvent emissions, we would be interested to know why powder clearcoats are not more widely used.
The Bavarian company BMW was the world's first car maker to use powder clearcoats in a big way and are currently coating 500 car bodies a day. The powder is supplied by DuPont Performance Coatings (DPC), who have overcome the disadvantage of limited resistance to weathering that conventional polyester binders offered. DPC's powder clearcoat is based on a functional epoxy acrylic resin. It is thermally cured with the aid of a carboxy-based hardener. The rheological properties of this chemical basis are the key to the excellent flow and resultant smooth surface finish. The ideal granulometric distribution of the powder particles is said to be another major parameter. Particles over 50 mu in size are cut off, but the proportion of fines (particles less than 5 mu in size) must not be allowed to become too large either. The particles size distribution must consequently be very carefully adjusted in order to obtain an optimum compromise between application of the powder and its flow.
The powder is applied with electrostatic spray guns in the normal way and cured at 140°C for 30 min. The thickness of the cured coating at BMW is currently 60 ± 7 mu. As already mentioned, acrylic clearcoats are characterized by particular resistance to weathering, as well as chemicals and scratching. An OEM material must meet the extreme requirements imposed by the automotive industry. The surface finish of a clearcoat is expressed in terms of its wavescan values. The longwave values, in particular, yield results of between three and five units for horizontal surfaces and eight to ten units for vertical surfaces. Between 85 and 87 units are obtained for the gloss.