Outgassing Phenomenon in Reaction Injection Molded Parts

Three stages involved in the RIM process are impingement mixing of di isocyanate and polyol, filling and curing in the mold, and postcuring in a separate oven to achieve complete conversion of diisocyanate. Traces of water in the polyol react with diiso cyanate, and generate CO ₂ in a side reaction during mold filling and curing. It may not be possible to postcure the RIM part immediately after curing. During that period, known as floating time, moisture in ambient air reacts with residual diisocyanate generating addi tional CO ₂ . Part of the CO ₂ diffuses out during the floating period, and the remaining CO ₂ evolves during postcuring. If these gases are not completely removed from the part during postcuring, they can "pop up" on the surface in the paint baking oven, creating unaccep table surface quality. This phenomenon is called "outgassing," and is investigated in this work.