HEAT-SENSITIVE RECORD MATERIAL AND MICROCAPSULE

The invention describes a heat-sensitive record system employing capsules formed of excess polyisocyanate compared to the stoichiometric quantity needed for encapsulation. The microcapsules comprise an integral outer wall material and an open-pore sponge-like networked core extending from the wall material into the microcapsule and defined by a plurality of substantially discrete but extensively interconnected void spaces, a core material filling said void spaces, said microcapsule being a reaction product of an excess, compared to a stoichiometric amount for effecting encapsulation, of a polyisocyanate having a functionality greater than two with an active hydrogen-containing compound, said microcapsule being of less than 500 microns diameter and having a void volume of from 60% to 80% by volume.