Ronald M. Herrington

Tailoring the Performance of Molded Flexible Polyurethane Foams for Car Seats

The automobile seat is a major element of contact between the occupant, the vehicle and ultimately the road surface. Flexible polyurethane foams are the material of choice for this application, not only because of the economies offered by large scale operations, but also because the cushioning characteristics of the foam/seat assembly can be adjusted. Commercially useful foams can be made from a variety of polyurethane molding chemistries. Recent advances in polyol and copolymer polyol technology, together with multiple isocyanate choices and even new foam manufacturing technologies, present the foam producers, seat assemblers and seat designers with a myriad of options. The automotive original equipment manufacturers (OEMs) worldwide are looking for optimization of the balance between foam weight and foam specifications, with more emphasis than ever on comfort and durability. This goes with specific requirements for the various foam pads, i.e., front cushion, rear cushion, front back-rest and rear back-rest. This paper presents new data showing how the choice of molding chemistry impacts not only foam processing and physical properties, but also the comfort and durability that can be expected from the final seat assembly. Results from recent studies carried out by The Dow Chemical Company on a global basis and concentrating on static and dynamic fatigue, resiliency, vibration damping characteristics and humid aging, are presented in an effort to provide foam producers and users worldwide with up-to-date information useful in helping them to meet their present and future performance targets.

Endurance of Polyurethane Automotive Seating Foams under Varying Temperature and Humidity Conditions

The long-term comfort and durability properties of the flexible molded foams used in many forms of transportation seating are a subject of increasing interest to foam molders and seat producers. Existing and proposed new specifications for load bearing and other fatigue losses have necessitated a new look at the fundamental understanding of why foam properties change with temperature and humidity. In previous papers we have demonstrated the broad range of performance that can be expected from the well established and finely tuned chemistries (Hot Cure, TDI HR, MDI HR and TM-20 HR) currently used to make molded seating foams all around the world. Our focus turns now to a more fundamental study of the mechano-sorptive properties of these alternative foams in order to understand the mechanisms by which temperature and moisture cause changes in the foamed polymers. It was postulated that by knowing the exact sites of the water attack on the polymer, new ideas for improving important performance characteristics like wet compression set and tropical fatigue would arise. To get to the details of how temperature and moisture affect the mechanical response of a polyurethane network, we studied compression sets over a wide range of conditions and correlated those data with morphology changes obtained from spectroscopic studies and with traditional dynamic fatigue tests conducted in similar conditions. Additional insight into the reorganization of the polymer networks was gained from detailed analysis of the foams dynamic mechanical performance under the influence of transient moisture conditions. We are now able to present a more comprehensive picture of the mechanisms behind the phenomena of wet compression set and tropical fatigue. This knowledge will be helpful to those striving to develop new raw materials and formulations for the next generation of transportation seating foams.

High Resiliency Polyurea Foam-An Improved Flexible Foam Matrix

It is likely that the development of urea technology for flexible seating foam applications has been hindered simply by a perceived incompatibility between the rapid isocyanate-amine reaction and the traditional «long» gel time foam processing requirements. We will show that the amine-isocyanate reaction rate can be controlled, thereby making urea technology useful in flexible foam applications. Conventional processability evaluations on low pressure metering equipment have shown that amine terminated polyether resins can be used in place of conventional polyols in typical foam formulations without jeopardizing desirable processing parameters. In addition, nonpolymer polyol reinforced polyurea foam matrixes have hardness properties comparable to or better than conventional polymer polyol filled urethane foams