Quantitative evaluation of internal mold release agents for polyurea RIM by the measurement of the release forces

The measurement of mold release forces has been used to evaluate an internal mold release (IMR) agent for polyurea RIM. Two molds were designed so that the entire release area consisted of shear release. One mold consisted of parallel plates mounted on a rheometer which rotated to give shear, while the other consisted of a rod and pipe where pull-out force was measured. Release forces from both molds agreed under the conditions examined. Mold release forces were mapped out as a function of molding conditions and IMR concentration. The polymer made was a 39% hard-segment polyurea system based on Jeffamine D4000, diethyltoluenediamine, and a uretonimine-modified diphenylmethanediisocyanate. Zinc stearate was the IMR. Molding conditions examined were 25-138°C mold temperature, 30 s to 10 min demold time, and 0-2% zinc stearate. The presence of zinc stearate reduces release forces by over 80%.