In RIM-process

In RIM processes, two or more reactive components are mixed together, starting the reaction between the components before the mixture is dispensed into the mold. This tends to increase the viscosity of the liquid that is dispensed due to an increase in molecular weight of the polymers or pre-polymers formed in the initial reaction. An increased viscosity can prohibit complete filling of the mold and permeation of the preform. This tends to decrease the adhesion between the matrix and the fibers. Poor interfacial adhesion between the reinforcement and matrix phase can cause a material to have less than desirable stiffness and strength. 

Since mold pressures in RIM processes are usually below 100 psi (0.69 MPa), mold-clamp-pressure requirements can accordingly be low. Most RIM equipment is in the 25-100 ton range. Depending upon production quantity and quality requirements, molds for RIM may be made from aluminum-filled epoxy for low production, or from cast or machined aluminum or chrome-plated steel for longer runs. Molds must be heated to 120-160°F (49-71°C). Applications include automobile bumpers, radio and TV cabinets, furniture and business-machine housings (5). 

High conversions and molecular weights are obtained because reversible reactions and side-product removal is not an issue. In RIM processes, liquid monomers are mixed using impinging jets and must quickly flow into the mold before the reacting mixture becomes too viscous. The complete cycle time for injection, reaction and umnolding (so that the mold can be used to make the next product) is often only 30-60 s. RIM is used to produce rigid molded polyurethane automobile parts and polyurethane foam seat cushions [3j. 

Dicyclopentadiene is also polymerized with tungsten-based catalysts. Because the polymerization reaction produces heavily cross-Unked resins, the polymers are manufactured in a reaction injection mol ding (RIM) process, in which all catalyst components and resin modifiers are slurried in two batches of the monomer. The first batch contains the catalyst (a mixture of WCl and WOCl, nonylphenol, acetylacetone, additives, and fillers the second batch contains the co-catalyst (a combination of an alkyl aluminum compound and a Lewis base such as ether), antioxidants, and elastomeric fillers (qv) for better moldabihty (50). Mixing two Uquids in a mold results in a rapid polymerization reaction. Its rate is controlled by the ratio between the co-catalyst and the Lewis base. Depending on the catalyst composition, solidification time of the reaction mixture can vary from two seconds to an hour. Similar catalyst systems are used for polymerization of norbomene and for norbomene copolymerization with ethyhdenenorbomene. 

Unlike polyurethane-RIM processes, nylon-RIM reactions are endothermic and require temperatures of 130-140°C. In contrast to the polyurethane-RIM systems, this enables thick wall parts to be made. Cycle times of 2-3 minutes are comparable to those for polyurethane-RIM. In the development stage, current work is concerned with reducing moulding times and optimising moulding conditions. 

The RIM process was originally developed for the car industry for the production of bumpers, front ends, rear ends, fascia panels and instrument housings. At least one mass-produced American car has RIM body panels. For many of these products, however, a number of injection moulding products are competitive, including such diverse materials as polycarbonate/PBT blends and polypropylene/EPDM blends. In the shoe industry the RIM process has been used to make soling materials from semi-flexible polyurethane foams. 

Interest in the RIM process appears to have abated somewhat in the 1990s. Nevertheless, nearly 100000 tonnes of polyol and polyisocyanate were consumed for this application in the USA alone in 1993. 

The basic RIM process is illustrated in Fig. 4.47. A range of plastics lend themselves to the type of fast polymerisation reaction which is required in this process - polyesters, epoxies, nylons and vinyl monomers. However, by far the most commonly used material is polyurethane. The components A and B are an isocyanate and a polyol and these are kept circulating in their separate systems until an injection shot is required. At this point the two reactants are brought together in the mixing head and injected into the mould. 

Since the reactants have a low viscosity, the injection pressures are relatively low in the RIM process. Thus, comparing a conventional injection moulding machine with a RIM machine having the same clamp force, the RIM machine could produce a moulding with a much greater projected area (typically about 10 times greater). Therefore the RIM process is particularly suitable for large... 

In the reinforced RIM (RRIM) process a dry reinforcement preform is placed in a closed mold. Next a reactive plastic system is mixed under high pressure in a specially designed mixing head. Upon mixing, the reacting liquid flows at low pressure through a runner system to fill the mold cavity, impregnating the reinforcement in the process. Once the mold cavity is filled, the plastic quickly completes its reaction. The complete cycle time required to produce a molded thick product can be as little as one minute. 

Currently, the process can only be used for desulfurization of oil in the refining industry. This technology is included in RIMS without the express approval of the developer. It is included because the technology could have application for remediation in the future. 

Smith Environmental is the owner of the battery waste treatment process (BWTP), a technology that uses washing, liberation, and gravity separation to treat waste from battery wrecking operations. Treatment by the BWTP process typically yields rubber, plastic, and a concentrated lead product. The vendor claims this is a closed-loop system where all water used in the process is recycled. The technology was commercially available and had been used for full-scale cleanups in 1995. RIMS were unable to obtain information from the vendor, so current commercial availability is unknown. 

In this review of LCM we will try to be general when possible, but we are forced to specialize to the RTM process in many cases. In particular the special features of the S-RIM process (high-speed mixing, materials, etc.) are almost completely left out of the discussion. For readers with a special interest in this topic we recommend the book by Macosko [3]. 

Epoxy resins are an important class of polymers used for reactive processing. However, it is rather difficult to find a formulation which provides sufficiently high process rates to be useful in the modern processing equipment used for the RIM-process. 

The so-called RIM-process (reactive injection molding) is a current realization of the reactive molding process. The heart of the process is the shock mixing of the reactive ingredients, which is achieved by collision of two jets injected at a pressure of 10 - 20 MPa. The reactive mixture is injected into the mold in a laminar flow regime the pressure at this stage does not exceed 0.1- 0.4 MPa.259 The practical development of this method relies on automatic control systems and modem high quality equipment. 

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