CONVECTIVE AND RADIANT (IR) CURING OF BULK AND WATERBORNE EPOXY COATINGS AS THIN-LAYERS - PART-1 - METHODOLOGY

A method for studying the curing of 100 mu m-thick epoxy-based layers coated on steel substrates is described. A simple waterborne epoxy rea ctive system based on a diglycidylether of bisphenol-A prepolymer and with a polyether triamine was set up by emulsifying the epoxy resin wi th the use of an ethoxylated-nonylphenol emulsifier. The particular ph enomena involved during the isothermal curing of such an epoxy emulsio n were decomposed by considering the same formulation without water an d without water + emulsifier. The chemical kinetics were determined by DSC and by size exclusion chromatography. As previously proposed for numerous epoxy-amine reactive systems, for the three types of coatings , a second-order autocatalytic law was able to interpret the data. The presence of water delays the gelation characterized by rheological me asurements. As a consequence, the epoxy conversion at the gel point in creases. This phenomenon can be related to the inhomogeneous polymeriz ation process during which the epoxy groups can be trapped into the in itial epoxy particles. In addition, the microdielectrometry technique was used to follow the curing degree of the epoxy reactive system of t hin layers during the drying and curing processes under radiant heatin gs such as infrared curing.