The field of this invention relates to flexible polyurethane foams and, particularly, to flexible polyurethane foams which have a reduced tendency to drip when exposed to flame.
The preparation of flexible polyurethane foams from polyols and isocyanates is well known. Polyurethane foams burn easily and, accordingly, the incorporation therein of various flame retardant materials is conventional. The mere incorporation of flame retardant additives does not, however, reduce the unfortunate tendency of polyurethane foams to melt in contact with flame and to drip melting fragments.
Attempts have been made to overcome the melting or dripping tendency of polyurethane foams upon exposure to flames, but such attempts have not succeeded to an appreciable extent. The problem apparently lies in the fact that most attempts to prevent polyurethane foam from dripping upon exposure to flame involve the addition of foam precursors or additives to the foam which do not provide a homogeneous coherent foam. Accordingly, there is a need for providing a polyurethane foam which has a reduced tendency to drip upon exposure to flame.
A distinction must be made between the problems involved in flexible polyurethane foams and rigid polyurethane foams upon exposure to flame. Rigid polyurethane foams do not drip upon exposure to flame. The very structure of a rigid polyurethane foam enables the manufacturer to incorporate therein higher amounts of fillers and flame retardants than can be incorporated in a flexible polyurethane foam. Were a manufacturer of flexible polyurethane foam to incorporate all of the various filler and additives which may be added to a rigid foam, the flexible flame would lose its flexibility. The manufacturer of rigid foam does not have to consider loss in flexibility upon incorporation of high amounts of additives. Prior attempts to prevent flexible polyurethane foam from dripping resulted in the lowering of the physical properties because of addition of high amounts of fillers, and the foam thus produced was of a high density which had reduced flexibility and usefulness.