Quantitative determination of mar resistance of high gloss coatings

Abstract

Nowadays, ones are prone to purchase consumer products on their esthetic aspect as much as functionality. Even if minor surface damages are formed, it might deteriorate the original appearance of the surface and lower the esthetic satisfaction. Common surface damages include cracks, delamination, and scratch/mar arising from mechanical abrasion. As one of protective layers, high gloss coatings are gradually getting more attention for both esthetic and functional applications. In particular, housings of consumer electronics, cases of cellular phone, as well as interior parts of automobile are fabricated with high gloss surfaces to provide a luxury sensation and emotional quality. Therefore, any subtle surfaces damages (i.e., mar and scratch) on the coatings are absolutely undesirable. A mar is a mark caused by a sliding contact, which is too minute to be perceived by the naked human eyes alone. Nevertheless, mar becomes visible with its large quantities present and/or with an observer in different angle views. An example is typical damage found on car bonnet after an automatic car wash, which is damaged by a relatively low level of applied load. On the other hand, scratches are regarded as visible surface damages and grooves that the human eyes can perceive. The damages are commonly associated with surface deformation caused by a heavy sliding. Typically, this is brought about by a phenomenon termed “stress whitening” or “cutting” where the deformation is more severe than subtle mar damage. Many coatings industries have used to evaluate mar resistance using their own test methodology, such as the pencil hardness test, peel-out test, the knife test, etc.. However, these standards only emphasized the test methodology, without explicit description about quantitative determination of the mar damage on coating surfaces. It is non-trivial to quantitatively evaluate the degree of subtle surface deformation (i.e., mar damage). The main aim of the current study is to explore the mar behavior under a low mechanical abrasion condition. The effectiveness of a new approach for evaluating the mar resistance of high-gloss coatings is demonstrated. The observed mar behavior is correlated with the changes in gloss and luminance in relation to surface roughness.