Over Basecoat Systems COB

The pigmented basecoat is formulated on either a highly durable solvent based polyester, or an aqueous acrylic dispersion. 

Critical to formulating a successful metallic basecoat is the selection of aluminium paste. In general the larger the particle size of the flake, the better the lustre. A polyethylene wax dispersion is also incorporated into the formulation to aid metal control and lustre. The binder in solvent based systems is a durable saturated polyester cured with a melamine formaldehyde resin and modified with CAB, to assist in film setting and hardness. 

Solvents used in basecoats must be fast evaporating, e.g. ethyl, butyl acetate or MEK. This is essential so that the metal particles set randomly and do not have time to flow out or orientate. Slow evaporating solvents result in dull lustre effects. 

Coloured metallic basecoats are formulated using strong transparent light fast pigments predispersed in the polyester. 

The basecoat is thirmed to a spray viscosity of 15-20 secs Ford No. 4 Cup, with fast evaporating solvents and this is applied in 2 thin coats, and allowed to dry for at least 15 minutes prior to application of the thermosetting clear overlacquer. 

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