Modeling of the continuous thermal drying process of epoxy coatings

Drying of thin epoxy varnish/glass cloth composites (prepregs) is the first process in the manufacture of printed circuit boards. In the described industrial dryer prepreg based on a multifunctional epoxy/MEK varnish is dried by hot air at a cloth speeds of 10 m/min in a vertical oven of 30 m overall length. A uniform concentration model is presented which utilizes diffusion coefficients extracted from isothermal drying data using a free volume theory. This model allows to describe average residual solvent concentration and the coating thickness at any point during the drying process. The results are within 2% of the actual solvent concentration.