Cold-molded foam

Classification. Flexibie urethane foams have the largest market of all polyurethane products. The production properties and applications of various flexible urethane foams are described in the following sections. Flexible urethane foams are defined as open-cell urethane foams having the property of complete recovery immediately after compression. They can be classified into two kinds, i.e., polyether foams and polyester foams. Polyether foams are further classified as follows conventional flexible foams, high-resilience flexible foams (HR foams), cold-molded foams, super-soft foams, and viscoelastic foams. 

The molded foam process can be classified into two types—the hot-molded foam process and the cold-molded foam process. The two processes are classified by the molding temperature and oven temperature. 

HR foam (high-resilient foam) is sometimes classified as a cold-molded foam because it can be molded at low temperatures. However, HR foams have slightly different formulations than standard cold-molded foams. There are many kinds of molded-foam formulations in the literature. The following formulations are only a few examples. 

Hot-Molded Foam and Cold-Molded Foam. Hot-molded foams are jH oduced by using either conventional polyeflier polyols (3,000 MW,... 

Cold-molded foams, however, are prepared by using formulations based on blends of MDI and TDI, or 100% MDI, because the co-use of MDI with TDI makes it possible to use low oven and mold temperatures due to the faster reaction of MDI. The MDI can be either pure MDI, modified liquid MDI, or polymeric MDI. Some confusion may arise between cold-molded foam and high-resilience (HR) foam. 

In recent years, HR foams have been prepared by using almost the same molding conditions as cold-molded foams, i.e., low mold temperature using the MDI-TDI blend formulation. However, in the development stage of HR foam, only TDI-based formulations were used, which required hot-mold conditions. For these reasons HR foams are not exactly equal to cold-cure foams. However, in recent years, HR foams have been produced by blends of MDI and TDI. The resulting foam systems can be molded at the same molding conditions as those for cold-molded foam systems. 

In comparison with cold-molded foams, hot-molded foams have disadvantages of higher mold temperatures and longer mold-retention times, but have the following advantages higher ratio of load-bear-ing/density, lower cost, and easier molding of complicated products. An example of a formulation of hot-molded foams is shown in Table 19. 

Material Family Injection Compression Hansfer Casting Cold Molding Coating Structural Foam Extrusion Laminating Sheet Forming RP Molding FRP Filament Dip and Slush Blow Rotational... 

Molded flexible foam products are becoming more popular. The bulk of the molded flexible urethane foam is employed in the transportation industry, where it is highly suitable for die manufacture of seat cushions, back cushions, and bucket-seat padding. TDl prepolymers were used in flexible foam molding in conjunction with polyether polyols. The need for heat curing has been eliminated by the development of cold-molded or high resiliency foams. 

The mechanical characteristics of the epoxy and polyester cold-cured syntactic molded foams do not differ much from the hot-cured materials (Table 12)1),... 

C02 blown foam - A polyurethane foam in which all of the gas from expanding or blowing is carbon dioxide (CO2) generated by the chemical reaction between water and isocyanates also called water-blown foam (3). cold-cure foam - See Cold molding. 

PU foams were prepared by the one-shot, free-rlse method. A homogeneous liquid mixture consisting of Nlax 31-28, Isonol-100, silicone surfactant DC-193 (Dow Corning), T-12, Nlax A-1 (Union Carbide), trlchlorofluoromethane (Freon llA, E.I. duPont de Nemours Co.), and water was mixed thoroughly with Isonate-143L. It was put Into a cold mold and allowed to free rise. 

CCRIS 7738 EINECS 204-126-9 Ethene, tetralluoro- Ethylene, telrafluoro- Ruoroplast 4 HSDB 844 M 122 Perfluoroethene Perfluoroethylene Tetrafluoroethene Tetrafluoroethylene 1,1,2,2-Tetrafluoroethylene TFE UNI 081. Release agent, dry lubricant for use on cold molds, esp. for epoxy potting/encapsulating, PU, nylon, acrylics, PP, PC phenolics, PS, foams, rubber molding. Gas mp = -142.5° bp = -76.9° d = 1.519 insoluble in H2O. 

The need for heat curing has been eliminated by the development of cold-molded or HR foams. These molded HR foams are produced from highly reactive polyols and are cured under ambient conditions. The polyether triols used are of molecular weight 4500-6500 and are high in ethylene oxide (usually >50% primary hydroxyl content). Reactivity is further enhanced by triethanolamine, liquid... 

As a direct consequence of equipment requirements such as venting or automatic opening and closing of the mold, or formulation aspects such as faster reacting times, molded flexible PU foam production is quite more complex than that of slabstock foams and considerably more expensive. Depending on the type of curing, two major mold-foaming processes are industrially available the hot-cure and the cold-cure. 

Process particulate pickup may significantly increase the risk of boiler foaming. This kind of problem happens in the crossover of hot to cold water during manufacturing processes, as in rubber tire factories, food can cookers and retorts, plastic injection molding, and the like). 

Cold curing permits the formation of dual density foam products. We either sequentially inject different formulations or we mold the first foam then mold the second around or on top of it. When making dual density foams, it is important that the first component develop a continuous skin prior to the injection of the second reactive mixture. 

The novolac foams are made by mixing the solid (powdered) oligomer (70 parts), carbon filler (30 parts), and hardener (hexamethylenetetramine) in a vibromixer and then press-molding the mixture for one hour at 150 °C, at a compression of 30-40% of the initial volume39). Casting compositions curable at room temperature are made from resol cold hardening oligomers 83). 

A release agent, such as polyethylene waxes, is used if the mold must be stripped away when cold. In this case the foam comes away from the... 

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