Annealing profile and UV exposure effects on network development in UV curable powder coatings

摘要

Four novel polymers were synthesized and formulated into clear powder coatings. The polymers were applied as powder cast films and evaluated for optimum film formation conditions, curing profiles, and coatings property development. The polymers were characterized by acid value titrations, gel permeation chromatography (GPC), nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), rheology, inclined plate flow, and contact angle. The processed powder coatings were applied to cold rolled steel substrates, subjected to thermal energy for annealing, and irradiated by UV light to affect crosslinking. The cured polymer films were evaluated via basic coatings tests such as smoothness, film thickness, gloss, impact resistance, flexibility, pencil hardness, crosshatch adhesion, and MEK rub resistance. Dynamic mechanical analysis (DMA) and DSC were sued to evaluate the degree of cure, crosslink density, and the effects of varying thermal treatments on polymer network formation. Crosslink density was shown to be relatively independent of the level of radiation, specifically the number of passes, when the annealing times and temperatures were identical. DMA analysis verified that annealing profiles were critical for achieving high crosslink density.