PERFORMANCE OF POLYESTER AND MODIFIED POLYESTER VERSUS PVDF COIL COATINGS

摘要

Coil coating is a continuous strip coating technology, which enjoyed rapid growth, and nowadays paints of different nature are applied this way on a range of metal substrates, for a large variety of products and uses. Technological developments of oil-free polyester based coatings, with suitable pigments and additives, allowed to produce coatings with similar characteristics to those of silicone modified polyester and near to those of some poly (vinylidene fluoride) - PVDF coatings. Fluoride hydrocarbide based products (with PVDF resin) give rise to coatings with excellent colour and gloss retention. In this work, the behaviour of polyester and silicone polyester coatings is compared with that of poly (vinylidene fluoride) coatings, all of them applied on hot dip galvanized steel. Coatings of two different colours (blue and brown) were studied for each paint system. These coatings have been exposed in two atmospheres (natural and artificial) with high ultraviolet radiation and, visual inspection of coating defects, colour change, gloss reduction and chalking evaluations, were carried out. In order to explain their corresponding performance, chemical changes on coil coating exposed surfaces were studied by Photoacoustic Spectroscopy associated to Fourier Transform Infrared Spectroscopy (PAS/FTIR).