WEATHER AGEING MECHANISM AND METHODSTO IMPROVING AGEING RESISTANCE OF COATINGS

摘要

Coatings (especially organic coatings) which are exposed to atmospheric conditions mayrnundergo weather ageing, resulting in some defects, such as loss of gloss, chalking, fading, yellowing,rnpeeling and cracking, etc. Weather ageing mechanism of coatings is analyzed briefly in this article.rnMain reasons for ageing are solar irradiation, environmental temperature and humidity. Among allrnthese factors, Ultraviolet (UV) is the most important reason for ageing. UV radiation in the rangernbetween 290 and 400nm carry energy from 314 to 419 KJ/mol, their high light energy could causernchain ruptures in organic compounds, resulting in degradation of polymers. Different binders lead torndifferent ageing characteristics. Ageing resistance of several common used topcoats, such as alkydrncoating, acrylic coating, acrylic polyurethane coating, fluorocarbon coating and polysiloxane coatingrnare also compared in this article.rnMethods of improving ageing resistance of coatings are also proposed. Select high bond-energy organicrncompounds as coating binders. Select inorganic pigments to reflect or scatter UV radiation. AddrnUV-absorbents and light stabilizers to reduce irradiation, improving ageing resistance and durability ofrncoatings. Apply integrative coating system, including primer, intermediate coat and topcoat. Sometimes,rnfinishing varnish is even used.