Clear Coats: how to achieve the next leap in performance
Richard RAABE - PPG (USA) Automotive Clear Coat Product Manager Jean BARJOT - PPG (France) Technical Director Automotive Decorative Systems

BASF

Dr. Karl-Friedrich DOESSEL – DUPONT (Germany)
Director Technology and Product Planning

Implementing an economic manufacturing process for Pearl-White at VCC Peter Larsson (Volvo) and Karl-F. Doessel (DuPont)

Pearl White has become a popular colour on luxury cars especially in America and Asia. The common process to manufacture this colour effect is based on two passes in the topcoat section of the paintshop: in the first pass solid white basecoat and clearcoat are applied and baked. In the second pass the transparent pearl basecoat and another layer of clearcoat are applied and baked. In most cases materials used are solventborne. This process tends to have lower first run OK rates (FTT) than other colours, has much higher material consumption, and creates high solvent emissions. Many trials have been made with a new waterborne process, where a standard white primer is used, baked and finished, followed by a wet-on-wet-on-wet application of a specially formulated white basecoat, transparent pearl basecoat, and clearcoat. Most developments failed based on intermixing of layers, which would have required the use of extensive flash-off between application steps (not fitting into existing lines) or poor sanding mark coverage. In a joint project between VCC and DuPont process conditions (paint flow, air flow, flash off, sanding operations) and paint material (rheology, atomization, and drying properties) were adjusted to allow this new process to be run in an existing line using robots and G1 Bell atomizers for the white basecoat, followed by an Eco pneumatic gun application of the pearl material. More than 5000 cars have been made and FTT rates have been improved to reach the level of other effect colours (silver) despite lower volumes. DOEs on process and material optimization will be shown.

Outlook on new technologies on scratch resistant clear coats
Jean-François ROLAND - BOLLIG & KEMPER (France) Technical Director

The design of automotive clearcoats with an improved scratch resistance and outstanding resistance against environmental elements, such as acid rain, UV degradation, high relative humidity and temperatures, is still a highly desired challenge. For a common clearcoat an enhancement in the resistance to chemical influences is usually connected with a loss in scratch resistance. Sol-gel silan technology promises excellent properties of both scratch- and chemical resistance. It is well understood that, highly crosslinked silan clearcoats, tend to be brittle and hence the shelf-life of sol-gel materials are too short for automotive uses. Furthermore, such compositions are very low in solid content, thus rendering the application where high filmsbuilds are desired, difficult. A new hybrid silan technology overcomes these difficulties and therefore poses no problems for the Automotive industry. This new technology doesn’t use the sol-gel process, so the material behaves like a common solventborne clearcoat. The hybrid clearcoat brings the desired scratch resistance in line with a higher chemical resistance already achieved.