Injection molding reactive

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. 

The most successful application of the RIM-process is in the production of polyurethane-based materials. Other systems, such as composites based on polycaproamide, epoxy resins, and unsaturated polyesters can also be processed by reactive injection molding. New reactive systems have also been specially created for the RIM-process260 because of the exceptional opportunities it offers for manufacture of finished articles from engineering plastics with a high modulus of elasticity and impact strength. The automotive industry, which is the main customer for RIM-articles, can utilize this technology to manufacture of massive parts such as body panels, covers, wings, bumpers and other made of newly developed plastics. 

The general requirements for compositions, that can be effectively used in the RIM process depend on the conditions of the main process operations, each of which imposes some requirements on the reagents in the reactive mix. The following list is an overview of these requirements  

Materials stable at temperatures up to 100°C, or even 150°C, which can be transported by pumping 

Two-component mixtures deviations from the stoichiometric ratio must not exceed 1 % 

TABLE 13.2 Comparison between Typical RIM and Thermoplastic Injection Molding (TIM)  

Experimentally it has been found that the Recrit for impingement mixing for onset of turbulence is around 140. This value seems to be insensitive to the impinging jet angle of incidence (82). Furthermore, the Re 3/4 dependence seems to hold until the range 140 Re 250 - 500 (83). 

From a process simulation point of view, in addition to impingement mixing, there are two main problems (a) nonisothermal and transient flow with chemical reaction, prevalent during the filling stage of the process, and (b) conductive heat transfer with heat generation due to the polymerization reaction. We discuss these two problems next, using the case of 

Domine and Gogos (88-90) considered a very long, very wide, and thin mold being fed by a constant temperature mixture of AA, BB molecules. Both types are bifunctional and the feed has a molecular weight Mq. The polymerization, assumed to be reversible, proceeds by the reaction of A-ends with B-ends, and follows idealized step polymerization (condensation) kinetics without the generation of a small molecule (91). Specifically, we have 

Setting (AA — BB) = Mx, we can write the general reversible condensation reaction 

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Polyurethanes differ from most other polymers in that polymerization frequently takes place at the same time that we are molding or forming them into a usable shape. The three most common processes of this type are reactive foaming, reactive injection molding (RIM), and reactive spray coating. 

Isosorbide polyurethanes, especially those based on aliphatic isocyanates, may be useful in the same applications as conventional polyurethanes i.e. thermoplastics, coatings, and foams. In fact, excellent rigid foams have been obtained from P(I-MDI)(5). Isosorbide has a low melting point of 61°C and it is suitable for use in reactive injection molding processes alone or in the form of a mixture with other conventional diols. In addition, its polymers may also find specific applications due to the anticipated high complexation ability of the two tetrahydrofuran rings in their isosorbide units. 

Rapidly solidifying compositions used for reactive injection molding place some restrictions on measurement. In the time required to prepare the reaction mixture, place a sample in the measuring cell of an instrument, and achieve a steady state in the sample and the measuring system at a preset temperature, chemical conversion of the material may advance considerably, making viscosity measurements meaningless. The volume of lost information depends on the ratio of the transient time necessary to achieve a steady state in the sample and the characteristic time of the chemical reaction. The sensitivity of the reaction rate to temperature is also important. In order to avoid the necessity to maintain isothermal conditions for the measurements, a non-isothermal scanning method for viscosity measurements was proposed.156... 

Figure 4.42. Scheme of the equipment used for reactive injection molding. 1 - reactor 2 - safety-valve 3 -mold 4 - piston-rod 5 - device for feeding a mold under pressure. 

Figure 4.70. Processability diagram (moldability) for the stage of mold filling in reactive injection molding dependence of material temperature (or average temperature on flow rate G). I - premature filling II - poor impregnation mixing III - flow instabilities.

This technology was first commercially applied to polyurethane blend [121] and patented as Rimplast (for Reactive Injection Molding), but many polymers have since been blended with polysiloxane thanks to this method polyethylene [122], polypropylene [122,123], polyamide [124-130], polyesters [128,131-133], poly(phenylene ether) [134], fluorocarbons [135] and many more. Many of them include reinforcing fillers such as fumed silica. The silicone base involved can moreover contain reactive groups such as the epoxy group [136,137]. A typical silicone base useful for these blends was de-... 

The term reactive processing is used to describe a polymer processing that involves chemical reactions. In principle, any processing operation can be conducted as a reactive process, viz. reactive injection molding (RIM). However, most often the term refers to reactive extrusion, and in particular, to the reactive compatibilization of immiscible polymer blends, usually conducted in a TSE. During the last 50 years, the latter machines have been used as chemical reactors for the polymerization, depolymerization (chemical recycling), polymer modification and compatibilization [Brown, 1992, Xanthos, 1992 Utracki, 1989, 1991, 1994, 1997]. 

High performance polyurethane elastomers are used in conformal coating, potting, and in reactive injection molding (or reaction impiugement molding) of IC devices. Furthermore, rigid polyurethane foams, most often in free-foam densities of 128—288 kg/m [8—18 lbs/ft (pc Q] useful for... 

Almost 15 thousand tons of polyurethanes were used as binders for sand in foundries in 1978 but the principal non-foam in sltu-polymerizatlon of urethanes was used for reactive injection molding (RIM) and reinforced RIM (RRIM) of relatively large automotive parts.— Comparable techniques without the use of a molding press were used for the production of mortars and for maxillofacial prosthodontlcs, i.e., the replacement of facial features. 

To the thermoset type belong bismaleimides and bisnadimides as well as oligomeric end capped imides. End capping occurs with reactive phen-ylethyl groups. These types are used for reactive injection molding and related techiuques. The chemistry of formation of the imide moiety is quite similar for both the thermoset type and the thermoplastic type. There are several monographs on PIs. Bismaleimides are a separate subclass... 

The term reactive processing is used to describe a polymer processing that involves chemical reactions. In principle, any processing operation can be conducted as a reactive process like reactive injection molding (RIM). However,... 

LIM Liquid impingement molding (now reactive injection molding, RIM)... 

LRMR Reinforced liquid reaction molding (now reinforced reactive injection molding, RRIM)... 

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