Reaction injection molding systems

The ring-opening metathesis polymerization of dicyclopentadiene was monitored by ultrasonic spectroscopy.16 The thermoset poly(dicyclopentadiene) is formed by ringopening and cross-linking in a reaction injection molding system. A reaction cell with a plastic window was constructed for use with pulse echo ultrasonic spectroscopy. Realtime measurements of density, longitudinal velocity, acoustic modulus and attenuation were monitored. Reaction kinetics were successfully determined and monitored using this technique. 

Finally, in the reaction injection-molding (RIM) process, low-viscosity reacting monomers or prepolymers are intimately mixed just before being injected into a hot cavity, where they react further and solidify. The RIM process, then, is a variation of the casting process, where highly reactive liquid systems are injected quickly, rather than being allowed to flow by gravity, into complex shape cavities, where they quickly react and solidify. 

Thermoset polyurethanes are cross-linked polymers, which are produced by casting or reaction injection molding (RIM). For cast elastomers, TDI in combination with 3,3,-dichloro-4,4,-diphen5lmethanediamine (MOCA) are often used. In the RIM technology, aromatic diamine chain extenders, such as diethyltoluenediamine (DETDA), are used to produce poly(urethane ureas) (47), and replacement of the polyether polyols with amine-terminated polyols produces polyureas (48). The aromatic diamines are soluble in the polyol and provide fast reaction rates. In 1985, internal mold release agents based on zinc stearate compatibilized with primary amines were introduced to the RIM process to minimize mold preparation and scrap from parts tom at demold. Some physical properties of RIM systems are listed in Table 7. 

In reaction injection molding, the starting point for the conversion process is liquid chemical components (monomers, not polymers). These components are metered out in proper ratio, mixed, and injected into a mold where the finished product is formed. In reality, it is a chemical and molding operation combined into one system of molding in which the raw material is not a prepared compound but chemical ingredients that will form a compound when molded into a finished... 

Reaction injection molding (RIM) is a process where a controlled chemical reaction occurs in a mold after injection of the material components. Commercially, the process is used almost exclusively for production of polyurethane parts by injecting a two-component system of isocyanate and alcohol (Figure 14-54). Polyurethanes can be produced with a wide range of properties, from very low density foams to reinforced, structural components. RIM is widely used... 

R. Dominquez, "The Effect of Annealing on the Thermal Properties of RIM Urethane Elastomers," in Reaction Injection Molding and Fast Reaction Systems (ed. J. Kresta) Plenum Press, New York, 1982. 

The successful utilization of Reaction Injection Molding (RIM) to fabricate complex polyurethane shapes In a single step from relatively low viscosity streams has led to a search for other chemical systems which can be fabricated by the RIM process. The rapid polymerization of molten caprolactam by anionic catalysis has been utilized to develop attractive nylon RIM systems. The incorporation of a rubber segment In the polymer chain allows the fabrication of high Impact or even elastomeric nylon parts. The combination of a rubber phase with the high melting (215°C) crystalline nylon phase provides useful properties at low temperatures as well as at elevated temperatures. 

Although the product of this early technology was a molten polymer, the rapid polymerization and high molecular weight polyamide product are clearly desirable qualities for a reaction injection molding (RIM) system. 

Anionic polymerization of nylon-based polymer systems to produce finished parts directly from monomers or prepolymers can be carried out by several processes e.g., reaction injection molding, low-pressure casting, resin transfer molding, rotational casting. 

In reaction injection molding, fillers and the reacting mass of matrix may each participate in the reactions, forming systems with a combination of features derived from the high adhesion between components. Numerous variations of this process... 

Polymerization in such systems is based on the reaction of isocyanate with hydroxyl groups to form the urethane linkage-OrganometaI Iic compounds (especially organotin) are often used to catalyze this reaction in commercial applications such as Reaction Injection Molding. Formation of elastomers with good mechanical properties is dependent on both reaction kinetics and development of two phase morphology. 

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