Reaction injection molding of foam plastics is actually a combination of chemical process and injection molding process. But compared with injection molding, it has two main differences: one is that the pressure of the mold used for reaction injection molding is very low, and the epp foam box makes the energy consumption and equipment cost of reaction injection molding system lower than that of conventional injection molding; Another is that the raw materials used in reaction injection molding are not pre configured compounds, but various chemical components that form compounds only after injection molding the parts.
　　During the reaction injection molding process, once the components are mixed, they react quickly and the material can solidify to the point where it can be demolded. Therefore, specialized raw materials and formulas need to be used, and sometimes the product also needs to undergo heat treatment to improve its performance.
　　RIM material polyurethane is widely used in the production of automotive baffles, protective plates, steering wheels, bumpers, air deflectors, mudguards, trunk covers, etc. due to its excellent mechanical properties.
RIM materials, properties, and applications, polyurethane RM and polyurea RM polyurethane RIM (PUR-RIM) are the earliest and most practical varieties developed. The raw materials used include polyols, isocyanates, chain extenders, and foaming agents.
　　The commonly used polyol is polyether polyol. In order to shorten the production cycle and meet the needs of large-scale production, polyols need to have high activity. The higher the content of primary hydroxyl groups, the higher the reaction rate, and the lower the content of impurities and unsaturated substances, the higher the activity. In addition, the viscosity of the material affects the collision and mixing effect between polyether and isocyanate, which in turn affects the RIM process and product properties. Generally, the higher the functionality of raw materials, the greater their viscosity; The higher the relative molecular weight of a polymer, the greater its viscosity.
　　Isocyanate is the main material to form polyurethane hard chain segment. with the increase of isocyanate symmetry, the crystallization ability, phase separation ability, elastic modulus, tensile strength, hardness and wear resistance of epp foam box are improved.