Study On Low Temperature Curing Epoxy Powder Coatings And The MDF Electrostatic Spraying Process

The thermosetting polymer powders coating is undergoing rapid growth as an ecological, economic and energyefficient technology. Powder coatings possess advantages over conventional coatings in that no polluting solvent loss occurs on application, flammability and toxicity are substantially reduced, owing to the use of electrostatic spray, little material is lost and, what is more, during baking, energy consumption can be reduced compared to solvent-borne or water-borne coatings.In this paper, two kinds of epoxy powder coatings were prepared by melting blending of phenolic resin/alkaline accelerator and micronized dicyandiamide (Dicy)/ 2-methyl imidazole (2-MI) as curing systems. The factors that affect the curing reaction and mechanical properties of epoxy powder coatings were investigated, such as amount of curing agent and accelerator. Then, the curing reaction and curing kinetics of this two different systems were investigated by non-isothermal differential scanning calorimetry (DSC), and the curing process was deduced. At last, the optimum amount of the curing systems and their curing conditions were determined. In addition, the effect of the technological parameters of electrostatic spraying for medium density fiberboard (MDF) on the one-pass transfer efficiency of powder were discussed by response surface analysis and the influence factors of coating flatting property were studied preliminarily.The experiment showed that for the epoxy-phenols system the optimum amounts of phenols and alkaline accelerator were respectively 10% and 1.0%. For this system the best curing conditions were curing 30 minutes at 120 degrees centigrade. And the cured layers had good mechanical properties. With regard to the epoxy-Dicy system, the optimum amounts of Dicy and 2-MI were respectively 2.5% and 0.25% and it should be cured 30 minutes at 130 degrees centigrade.A second order polynomial empirical models of the one-pass transfer efficiency of powder with the technological parameters of electrostatic spraying was set up by using Box-Behnken experimental design combined with response surface analysis. The effect of technological parameters on the one-pass transfer efficiency and their interaction were discussed. And the optimal technological parameters were determined. With the spraying distance of 134.5 mm, air pressure of 0.10 MPa and electrostatic voltage of 60 kv, the one-pass transfer efficiency of powder reached 56.7%.