Resilient foams

Commonly used isocyanates are toluene dhsocyanate, methylene diphenyl isocyanate, and polymeric isocyanates. Polyols used are macroglycols based on either polyester or polyether. The former [poly(ethylene phthalate) or poly(ethylene 1,6-hexanedioate)] have hydroxyl groups that are free to react with the isocyanate. Most flexible foam is made from 80/20 toluene dhsocyanate (which refers to the ratio of 2,4-toluene dhsocyanate to 2,6-toluene dhsocyanate). High-resilience foam contains about 80% 80/20 toluene dhsocyanate and 20% poly(methylene diphenyl isocyanate), while semi-flexible foam is almost always 100% poly(methylene diphenyl isocyanate). Much of the latter reacts by trimerization to form isocyanurate rings. 

There is an increasing market for higher resilience foams using the so-called polymer polyols. Amongst the earliest to become established were suspensions of styrene-aerylonitrile copolymer in the polyol. A variation involved some grafting of SAN, either instead of or in addition to the use of a suspension. 

In addition to freedom from bottoming out , most people prefer a seat which effectively provides a soft surface with a firm interior. One measure of the relationship between such surface softness and inner support is the sag factor or support factor. In one commonly used test this is obtained by dividing the force required to compress a foam by 65% of its height by the force needed to obtain 25% sample compression. This generally increases with density but is typically <2.5 for a conventional slabstock foam but >2.5 for a high-resilience foam. 

There is also growing interest in multi-phase systems in which hard phase materials are dispersed in softer polyether diols. Such hard phase materials include polyureas, rigid polyurethanes and urea melamine formaldehyde condensates. Some of these materials yield high-resilience foams with load deflection characteristics claimed to be more satisfactory for cushioning as well as in some cases improving heat resistance and flame retardancy. 

The two primary hydroxyl groups provide fast reaction rates with diisocyanates, which makes this diol attractive for use as a curative in foams. It provides latitude in improving physical properties of the foam, in particular the load-bearing properties. Generally, the ability to carry a load increases with the amount of 1,4-cydohexanedimethanol used in producing the high resilience foam (95). Other polyurethane derivatives of 1,4-cyclohexanedimethanol indude elastomers useful for synthetic rubber products with a wide range of hardness and elasticity (96). 

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. 

Flexible foam is made from long-chain diols with a small amount of triols for cross-linking to give strength and resilience. Foaming is produced by reaction between measured amounts of isocyanate and water to liberate carbon dioxide. Molded products are made by pouring the reactive liquid mixture into a mold cavity at 50°C. They foam and cure in 2-10 min, after which they are temporarily crushed or vacuum-shocked to open the cell walls and insure softness. Then they are allowed to condition for several hours to finish the cure. The major products are auto seating and headrests, and furniture cushions. 

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. 

High-Resilient Foam (HR Foam). HR foam is characterized by high ball rebound, low hysteresis loss and high sag factor. HR foam can be produced either as slabstock or as molded foam. 

In foam injection-molded parts the anooth-skinned resilient foam produces a tough energy-absorbing structure that is being used as a wood substitute in athletic products such as lacrosse-stick heads and hockey-stick blades. Protective structures for helmets and automotive parts are under development. All are being produced in densities ranging for 0.35 to 0.7 g/cc (22 to 44 Ib/ft ). In those applications where added sti ess is desirable the use of glass or titanate fiber reinforcement with the foamed structure is very effective (6). 

The transportation industry has many of the worldwide auto producers represented in seven Latin American countries. Brazil is the volume leader (over 1 million autos and trucks in 1979), followed by Mexico, Argentina, and Venezuela. These auto producers are rapidly adopting the concept of molded polyurethane foam seating including the superior cushioning of high resiliency foams. The pressure for increased fuel economy via weight rein Urethane Chemistry and Applications Edwards, K., et al. ... 

In Figure 17, the absorbance due to substituted ureas at 1645 cm" for the three formulation at early times of reaction are given as functions of time. These data are compared with the rise profile, gel profile and cell-opening times previously discussed, Figures 4-10. Concentrations of ureas are measurable from about the time of the peak rate of foam rise and achieve an apparently limiting value after about four minutes, about the time foam rise is complete. "Gel profile" appears to monitor structural developments in the foams which are occurring at the same time as the increase in urea concentration. In the "HR" formulation, onset of "gel" is delayed. This delay in onset of "gel" in high resiliency foams has often been observed (X, ]). 

No such delay, however, is observed in formation of diarylurea. While no direct measurement is yet available, it is taken that "gel profile" measures association of the polyureas into domains. In "HR" foams this domain formation is delayed, permitting larger, more completely aligned polyurea domains and accounting for the principal property characteristics which distinguish high resiliency foam 3). 

The creation of the autocatalytic high MW aminic polyols based on N-methyl substituted poly amines, represents an important development in the area of poly ether polyols for low-fogging flexible PU foams. The VORANOL VORACTIV polyols developed by DOW represent a revolutionary group of autocatalytic polyols with reduced volatile organic compounds (VOC) emissions in PU products, especially in high resilience foams for bedding and automotive seating [149, 150]. 

PIPA polyols, in spite of some disadvantages (tendency to foam shrinkage, and scorching), are used successfully for continuous slabstock flexible PU foams and high resilience foams (cold cure moulding process). 

ArceL [Arco] Polyethylene copolymers resins fa molded resilient foam pkg. 

Arpak. [Aico] Expanded polyethylene beads fw closed-cell resilient foam. 

Basotect . [BASF AG] Open-cell resilient foam plastic based on melamine resin used for soundproofing, thermal insulation with firei x)ofing characteristics. 

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