Joseph S. Sedita

Microscratching of Pmma on Flexible Substrates

The microscratch behavior of poly(methyl methacrylate) (PMMA) coatings on flexible substrates of cellulose acetate (CA) and poly(ethylene terephthalate) (PET) was evaluated using the NanoTest 550 microscratch device with a 3-micron radius, 60-degree conical-angle diamond stylus in ramped load from 0.3 to 10 mN. Tensile surface cracking was observed within 6–8 mN for all coatings regardless of coating thickness (from 0.2 to 3 microns). For the same coating thickness, PMMA on PET cracked at lower loads than PMMA on CA because of PET substrate deformation. Coating removal of PMMA was also found, but at higher loads following the tensile cracking. Onset of severe coating damage/removal in PMMA coatings was found to be dependent on coating thickness. The ranking of various PMMA coatings in terms of their extent of microscratching damage was comparable to their rankings based on Taber abrasion results. This suggested that only the severe coating damage on PMMA could be detected by the Taber abrasion test.