Cast polyurethane systems

Trimethylolpropane is a trifunctional monomer that can provide a unique crosslink density when used as a chain extender and curative with cast polyurethane systems. Usually, TMP (a triol) is used in combination with diols for curing MDHermi-nated prepolymers. Also, TMP is sometimes used to cure TDI ester prepolymers for low-hardness applications such as printing rolls. 

Wheels and tires are one of the major uses of cast polyurethane elastomers. We commonly see these on fork lift trucks and shopping carts, where their excellent abrasion resistance, resistance to oil, and good elasticity are valued. In industrial settings we find polyurethane covers on rollers used for paper, steel, and textile conveyor systems. In such applications, their excellent cut and abrasion resistance help prolong their useful life. If used in hot and humid conditions, polyether-based polyurethanes are preferred. 

It is most important to realize that at this time the full properties of the material are not yet developed, and the molded polyurethane has to be returned to the curing oven for the period recommended by the system supplier. The curing time varies depending on the chemistry of the system. The maximum properties of the cast polyurethanes are developed after a further 1 to 2 weeks at ambient temperature. 

Recently, the Maitland group has returned to a thermosetting polyurethane system, developed in-house [48], and combined the technology with superelastic Nitinol wires with electro-resistive heating [49, 50]. In the most recent embodiment, the SMP is cast around a Nitinol wire in its predetermined coiled shape (Fig. 4). The... 

Baytec, Polyurethane cast elastomer systems and prepolymers, Bayer Corp., Polymers Div. 

Baytit Polyurethane molded foam systems, Bayer Bayflex Polyurethane elastomeric RIM systems, Bayer Boytec Polyurethane cast elastomer systems and prepolymers, Bayer Betabrace Reinforcing composites, Dow... 

Turner, S. Richard, 1 Two-component (2-K), nonsagging, polyurea structural adhesive, preparation of, 255-256 Two-component (2-K) systems, 238-241 Two-component (2-K) waterborne polyurethane coatings, 206 preparation of, 254-255 Two-shot cast elastomer, preparation of, 249-250... 

Focusing collectors are usually cast acrylic Fresnel lenses, or mirrors of aluminized polyester film in frames of aluminum. These reflectors are either enclosed in a bubble of poly(vinyl fluoride) film, or under polycarbonate glazing, which may be covered with a fluorocarbon film to reduce the reflectivity. The absorbers for active systems are copper or aluminum since the temperatures are too high (325—370°C) for plastics. The frames, however, can be molded ABS, high density polyethylene or polyurethane, either solid or structural foam. Polybutylene or chlorinated PVC can be used for piping hot water, and tanks can be made of either reinforced polyester or blow- or rotational-molded, high density polyethylene (12—15). 

Polyurethanes based on MDI have the greatest flexibility in the choice of curatives and blends of curatives that can be used to obtained the desired properties. In cast elastomers, the hygroscopic nature of the curatives must be taken into account and proper handling and storage used otherwise, there may be a very high reject rate. Catalysts are also more readily used with the MDI materials. Organic acids such as adipic or oleic acids work better with TDI materials than MDI systems. 

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. 

Conathane . [Conap] Polyurethane elastomers cc ormal coating, potting and encapsulating system, casting system. 

Conoptic . [Conap] Polyurethane casting system for protot parts, windows, display deuces. 

Elastocoat . [BASF AO] Polyurethane casting and coating systems for mold making, tire filling, furniture edges, wear-resistant floor coverings. 

Hybri-Chem. [Hybti-Chem] Polyesto/ polyurethane hybrid system for open mold casting, lamination, spray appUc., resin transfer molding, tooling. 

Lnpraphcn. [BASF AG] Polyester poly for die prod, ci ptdyurethane, dwmioplastic grmules, textfie coating systems, finished parts made of polyurethane and casting elastomers for foe auKunotive, machine and equfo. construction industries. 

Pur-Fect Tool . [Ciba-Geigy] Polyurethane casting system used for assembly jigs, backfilling, core boxes, foundry gates and risers, laminating molds, mold cores, pattern plates, prototypes. 

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