Experimental study on the processing conditions of in-mold coating for injection-molded plates

In-Mold Coating (IMC) is novel coating method which achieves simultaneous injection molding and surface coating. In this paper, a mold for in-mold coating experiments was fabricated, which consisted of an overflow area, a coating channel, and sealing edges. The coating material used was two-component polyurethane with good transparency, high glossy, durability, and scratch resistance. The effects of the processing conditions of the in-mold coating on the bubbles and mixing characteristics in the injection molded plates were investigated. The bubbles that appeared over the substrate surface decreased, as the injected weight of the coating material increased. On the other hand, the bubbles increased with an increase of mass-flow rate. When the discharged flow rate was low, inhomogeneous surfaces appeared due to the poor mixing between polyol and isocyanate. It was found that the nozzle pressure of more than 180 bar was required to achieve uniform mixing.