Automotive,Molded Viscoelastic Foams

Abstract

An improved type ofmolded viscoelastic foam, Intellisense ^TM(Trademark of Woodbridge Foam Corporation), extends the effective operating range ofthe material from elevated temperatures to below 0 C, while maintaining the energy dissipation values at designed levels.

Until now, viscoelastic (VE) foams have not found a significant success in automotive interior/exterior applications due to an evident loss ofsome essential properties with changing conditions (e.g. diminished softness/ “friendliness” in contact with human body when used at low temperatures or reduced VE properties at high temperatures).

A viscoelastic behavior means a time-delayed and rate-dependent response to applied stress [Birley, A.W. et al. (1991). Physics of Plastics, pp. 260–261, Oxford University Press, New York, NY] and makes it desirable in parts designed for specific energy management (EM). However, to be acceptable for an application, the effectiveness of the foam response has to be in the expected usage temperature range of the final part. Systems formulated with a balanced mixture ofpolyols, some special additives, and modified isocyanates generated VE foams with the glass transition temperature (Tg) below 20 C. The observed loss ofviscoelasticity at elevated temperatures, common with prior-art foam of this type, is significantly reduced as well.

This novel approach to viscoelastic foams will benefit energy management automotive applications like head restraint, seat occupant safety, sound or vibration attenuation, etc. It is expected that this finding may extend the area of applicability beyond the car industry.

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