The Effect of Stress Absorbing Layers on the Wear Behavior of Painted Plastic Substrates

Erosion damage to automotive car bodies caused by stones and small sand particles and road debris significantly affects the appearance of paint. Painted engineering plastics as well as precoated sheet steel are affected by erosion phenomenon. Erosion of painted plastic substrates results in cosmetic concerns while that on metal substrates results in cosmetic to perforation corrosion. This work describes a laboratory simulation of erosion of painted plastic substrates by small particles on various paint and substrate types. Gloss loss was used to quantitatively evaluate erosion of painted surfaces. Wear behavior of painted plastic substrates to slag sand impact was evaluated as a function of several variables including paint type (one-component melamine crosslinked (1K) vs. two-component isocyanate crosslinked (2K)), thermal history, and coating modulus. The effect of slag sand type (particle size and chemical composition) was studied. Among the parameters that influence wear behavior, the effect of chip primer is also discussed. Failure characteristics are examined and related back to physical attributes of the system.

Based on this work, it is concluded that the best wear resistance (lowest gloss loss due to erosion and lowest number of gouges) is achieved with substrates topcoated with 1K paints baked at 116°C (on several types, compounded and reactor grades of varying modulus, of TPO). Adhesion promoter was flashed at room temperature (R.T.). Chip primer does not appear to have a significant effect on wear behavior, but in some instances, it helped reduce gloss loss and the number of gouges due caused by erosion. Further study of chip primer thickness effect is on resistance to erosion damage is currently being conducted.