UNDERSTANDING THE EFFECT OF PROCESSING CONDITIONS ON THE SCRATCH AND MECHANICAL BEHAVIOR OF AUTOMOTIVE PLASTIC COATINGS ON TPO

摘要

Scratching of plastic components has been a growing concern among automakers. Scratching may result from pre-delivery or post-delivery events. The coatings chemist may formulate differently for "green" properties, such as those correlated to pre-delivery, than for those properties resulting from aged, weathered coatings. Unfortunately, warranty cannot separate out which event is the more prevalent contributor to damage of coatings on plastics. While automotive coating producers measure such properties as tensile strength, modulus, and hardness in attempts to relate these mechanical properties back to the "green" scratch resistance, little has been done to show how mechanical properties change as a function of weathering.rnThis work attempts to correlate the scratch resistance behavior of different one-component (1K) crosslinked systems to the mechanical properties developed as a function of processing conditions and weathering. Of the parameters studied, cure temperature was found to be more critical than time at temperature, thus negating the concept of bake equivalents for coatings on plastics. In addition, it was found that forrnsome 1K cured coatings, scratch resistance did not change significantly with the processing conditions used, while mechanical properties did, especially after accelerated weathering.rnThis study indicates that the critical depth to fracture of flexible coatings is the most relevant indicator for determining scratch performance. This variance is important to consider since coatings on plastic are often softer than coatings on metal and the scratch is thus imparted deeper into the coating composite. As such, the influence of interfacial variances between the clearcoat, basecoat, and adhesion promoter on the coating's mechanical response to scratching was found to play a more prominent role in the resultant performance of these materials on TPO.