High-solids mar resistant clearcoats prepared from an isophthalate-based oligoester and a melamine resin. Study and characterization of mar resistance with scanning probe microscopy method

A new series of high-solids [low-VOC (volatile organic compound)content] mar resistant clearcoats (CL-series) were prepared upon crosslinking of a new-synthesized hydroxyl-terminated isophthalate-based liquid oligoester (L-311) with an hexakis(methoxymethylol)melamine (HMMM) resin, via an acid-catalyzed etherification reaction. The chemical, physical, and mechanical properties of the CL-clearcoats were compared to those of a reference clearcoat (CRO). An attempt was made to investigate the effect that the amounts of catalyst and melamine resin had on the clearcoats' physical, chemical, and mechanical properties, and moreover, to correlate these properties to the films chemical structures. The new-formulated high-solids clearcoats (CL-series) presented enhanced processability and higher NVW values (lower VOC content) than the reference clearcoat CRO, and their properties (pencil hardness, knoop hardness, adhesion, impact resistance, solvent and gasoline resistance, mar resistance, and flexibility) were better or comparable to those of the CRO. More specifically, the mar resistance of the CL-clearcoats series was investigated by applying both the crockmeter test and a novel method that employed a modified scanning probe microscope. In addition, we identified and characterized the different responses of the CRO and certain CL-clearcoats to marring stress. The experimental data regarding the mar resistance of the new-formulated clearcoats fully justified our polymer design strategy, verifying our expectations for the possibility of preparing glossy, high-solids mar-resistant clearcoats that could present enhanced processability and solvent resistance, relatively high pencil hardness, and at the same time very good elastic recovery to marring stress. (C) 2002 John Wiley & Sons, Inc. J Appl Polym Sci 83: 1317-1333, 2002.