Polymers are the building blocks of plastics, and how the polymer network responds to heat determines whether a plastic is a Thermoplastic or Thermoset. RIM is a Thermoset process.
RIM polyurethane systems are composed of two liquid components that chemically react to form plastic material in a mold.
The liquids, Isocyanate and Polyol, are commonly referred to as the “A Side” and the “B Side” components.
Generally, the “B” component contains additives such as stabilizers, flow modifiers, catalysts, combustion modifiers, blowing agents, filler, pigments, and release agents to modify physical characteristics in the final product.
When the “A” and “B” components combine they undergo an exothermic chemical reaction. To prevent scorching and/or part defects, cooling lines on the mold help dissipate this heat.
The RIM process utilizes:
- very low viscosity liquids ranging from 500 to 1500 centipoise (cps);
- low processing temperatures of 90 to 105 F°;
- low mold temperatures of 90 to 105 F°;
- and low internal molding pressures between 50 and 150 psi
The low viscosity, low temperatures and low pressures provide some very distinct benefits or advantages for the RIM process compared with other plastic processing methods.