Process for stabilizing by encapsulation red phosphorus to be used as flame retardant of polymeric materials and product so obtained

Claim 1

A process for stabilizing red phosphorus powder, in its various allotropic forms, by encapsulating the particles of said powder in a malamine resin for its safe use as a flame retardant of polymeric materials, which comprises the steps of: (a) preparing an aqueous solution of a melamine condensate cationized with a mineral acid by reacting in an aqueous medium melamine, formaldehyde, triethanolamine, and an aliphatic monohydroxyl alcohol having up to 5 carbon atoms, in the respective percent by weight ratios: 25.27% to 21.62%, 36.04% to 30.85%, 29.87% to 25.57% and 8.82% to 21,96%, and adjusting the pH thereof with the mineral acid; (b) forming a hydrodispersion of the solution formed in step (a) by dispersing red phosphorus powder directly therein; (c) heating said hydrodispersion, under stirring, at 80° to 100° C. to encapsulate individual particles of the red phosphorus powder by precipitating onto said individual particles of red phosphorus powder, said melamine condensate to form a continuous and compact layer of an insoluble, partially cross-linked melamine resin; and (d) subsequently drying the insoluble, partially cross-linked layer of melamine resin in an inert gas stream at 80° to 130° C. to obtain a cross-linked melamine resin-encapsulated red phosphorus powder suitable for easy and safe dispersion in polymeric materials, said layer of melamine resin which encapsulates said red phosphorus powder amounting to 0.1 to 30% by weight of the red phosphorus powder.