Effect of addition of hydrophobic nano silica on viscoelastic properties and scratch resistance of an acrylic/melamine automotive clearcoat

Scratches are a consequence of tribological events encountered by automotive coatings during their service lives. A series of analytical techniques such as laboratory carwash simulator, nano-indentation, tensile, DMTA, SEM, etc. were used in order to compare the effects of addition of various contents of a nano silica on changes in the viscoelastic properties and scratch morphologies of the resultant clearcoats. The results illustrate, that incorporating increased amounts of hydrophobic nano silica particles into an automotive clearcoat decreased its Tg whilst increasing its toughness. Increasing nano silica content also gave progressive transitions from fracture type scratches to plastic type scratches.