Process for manufacturing polyurea microcapsules and product therefrom

Abstract

Two embodiments of a process for producing concentrated suspensions of polyurea microcapsules especially suitable for manufacturing carbonless copy paper (CCP) are disclosed. Either embodiment can be a batch or continuous process. In the first embodiment, a liquid hydrophobic phase comprising a core material and polyisocyanate at least partially soluble therein is emulsified with an aqueous continuous phase including a polyhydroxylated colloidal stabilizer to form a suspension of microdroplets of the hydrophobic phase. A polyamine such as diethylenetriamine reactive with the polyisocyanate and a catalytic amount of an alkaline base are then added, initiating an interfacial polyaddition reaction at alkaline pH which forms the polyurea microcapsules. The alkaline base is preferably NaOH, KOH, or LiOH; the polyisocyanate is preferably a biuretized or isocyanurate-modified triisocyanate of a lower alkyl diisocyanate; and the polyamine is preferably added in a stoichiometric ratio relative to the isocyanate. The second embodiment is similar to the first, except that the alkaline base is added along with a surfactant having multiple S-containing substituent groups. Also, the colloidal stabilizer may be non-polyhydroxylated, such as polyvinylpyrrolidone. Microcapsules produced by either embodiment exhibit excellent properties of impermeability to the core material and freedom from agglomeration, even at high concentration and even during an optional curing step performed at elevated temperature. The microcapsules also exhibit excellent copy-forming ability, resistance to handling-induced rupture, and storability when used in CCP.