Weathering study of epoxy paints

The weathering characteristics of TiO2-based paints of diglycidyl ethers of bisphenol A (DGEBPA), bisphenol F (DGEBPF), bis-2,6-xylenol F (DGEBXF), bis-2,6-xylenol S (DGEBXS) and bis-2,6-xylenol (DGEBX) with various curing agents have been studied by subjecting them to accelerated and environmental weathering. Of all the epoxy resins, the paint using DGEBPA gave the best weathering characteristics with better chalk resistance, optimum yellowing and good gloss retention when cured with amine terminated dimer fatty acid-based polyamide. The methyl substitutions on aromatic ring and presence of methylene and sulfone groups between the phenolic moieties caused enhanced degradation of epoxy resins as evidenced by their faster chalking on exposure. When cured with an aminosilane compound all the epoxy paints showed excellent improvement in chalk resistance but were associated with poor initial gloss and more yellowing during exposure. The relationship between the two types of weathering was found to be approximately two and a half hours exposure in accelerated ageing being equal to 1 day in environmental weathering in Mumbai (India), thus leading to a nearly 10-fold acceleration of weathering. (C) 2004 Published by Elsevier B.V.