Fm. Mirabella et al., Theoretical analysis and experimental characterization of the TPO/adhesionpromoter/paint interface of painted thermoplastic polyolefins (TPO), POLYM ENG S, 40(9), 2000, pp. 2000-2006
Exterior and interior automotive applications of TPO (thermoplastic polyole
fin) resins, which are, often, composed of a paint coating over an injectio
n-molded TPO, have increased interest in the surface chemistry and physics
of TPOs. Specifically, the interface system composed of base-coat paint/adh
esion promoter/TPO is of primary importance in controlling the paint adhesi
on to the TPO. The major, active component in the adhesion promoter is a ch
lorinated polypropylene (CPO). A theoretical model based on phase thermodyn
amics and diffusion kinetics resulted in a prediction that the TPO/CPO inte
rface should have a lower bound thickness of about 11 nm and an upper bound
of about 400 nm. A battery of experimental strategies to characterize this
interface system was discussed. Techniques used were transmission electron
microscopy (TEM). atomic force microscopy (AEM) and scanning transmission
X-ray microscopy (STXM). The near-surface morphology of both unpainted and
painted, injection molded TPO plaques exhibited ethylene-propylene rubber p
articles close to the surface, i.e. within the first 0.1-0.8 micrometer of
the TPO surface, and no "overlayer" of transcrystalline polypropylene at th
e surface of the TPO. Each of these microscopic methods shaved that the adh
esion promoter/TPO interface was very sharp. The thickness of this interfac
e was measured with respect to the interdiffusion of the CPO and TPO by STX
M. The STXM measurements yielded an apparent interface thickness between th
e adhesion promoter and TPO of 340 +/- 80 nm. This was in good agreement wi
th the theoretical predictions.