Case Study: DuPont clearcoat gets the sag out, improves vehicle appearance
DuPont optimizes the rheology of clearcoats to improve the optical quality of car finishes.
Application Description
Automotive clearcoats are applied with a film thickness of 30-60 µm on horizontal and vertical areas of a car body. If the material has a standard, so-called Newtonian rheology, it tends to sag on vertical surfaces. This effect leads to inferior appearance on the verticals compared to horizontals. In the worst case, paint runs can be observed.
Materials Selected and Why
To prevent sagging, the clearcoat has to have a pseudoplastic rheology. This means it is more viscous if a low shear stress is applied. This behavior can be achieved by incorporating sagging control agents (SCA) into the main clearcoat binder. These particle-type ingredients form a sort of a network, which can be destroyed by shearing but which immediately recovers when the shearing ends. As a consequence, this paint has a low viscosity during application and immediately increases its viscosity on the car body, thus preventing sagging.
The binder modification is made in a special process in the binder manufacturing. Today, rheology-modified clearcoats have set a new standard for paint appearance and are used widely by all car manufacturers.
