A new class of high-solids low-gloss mar resistant pigmented coatings prepared from an isophthalate-based oligoester, a melamine resin and various talcs

Abstract

Talcs (3MgO.4SiO 2.H 2O) of various median particle diameters (2.20, 6.63 and 10.00 μm) were used as inert pigments (fillers) for the preparation of a novel series high-solids (low-VOC content) low-gloss mar resistant pigmented coatings (PN-series) where the binder was a new-synthesized hydroxyl-terminated isophthalate-based liquid oligoester (L-311) and the cross-linker an hexakis (methoxymethylol) melamine resin. The chemical, physical and mechanical properties [viscosity, non-volatiles by weight (NVW), knoop hardness, pencil hardness, impact resistance, flexibility, adhesion, solvent (MEK) resistance, gloss and mar resistance] of the new-formulated pigmented coatings were compared to those of their corresponding clearcoats and correlated to: (a) the curing conditions; (b) the amount of melamine resin; (c) the pigment's load; and (d) the pigment's particle size. For measuring the mar resistance of the pigmented coatings we applied the Taber Abrasion method and the inverse wear index, F [= I −1, cycles/cg (wear index I: weight loss (cg) per number of cycles)] was directly related to the mar resistance. The knoop hardness, the gloss (60 and 85°) and the mar resistance were the properties more seriously affected from the aforementioned variables. More specifically, the pigment's load and particle size seemed to affect more the 85° gloss and the mar resistance while the curing conditions and the amount of the cross-linker affected the knoop hardness, as well. In all cases the mar resistance of the pigmented coatings was the only of the film properties, dramatically affected from all the four aforementioned variables. The high-solids (NVW ∼70%) pigmented coatings (PN-series) presented excellent adhesion (5B), flexibility (>32%), impact resistance (160 inch-lbs.), MEK resistance (>200 rubs), very good mar resistance and low gloss at 60 and 85°. These results implied their suitability in various end-up uses (e.g. automotive dashboards) as they satisfy the modern industrial standards and demands for such applications.