Self-extinguishing polymeric compositions

Claim 1

A thermostable and self-extinguishing polyolefin containing an intumescent fire-retardant system comprised of a phosphorus constituent and a polymeric ethylene-urea condensation product as a nitrogen-containing synergist for the intumescent fire-retardant system, the system containing, as the phosphorus constituent, a product consisting substantially of (a) 75-99.5 wgt % pulverulent free flowing ammonium polyphosphate of the following general formula H.sub.(n-m)+2 (NH.sub.4).sub.m P.sub.n O.sub.3n+1 in which n stands for an integer having an average value of from about 20 to 800 and the ratio of m/n is about 1, and (b) about 0.5-25 wgt % of a water-insoluble resin encapsulating the individual ammonium polyphosphate particles, wherein the water-insoluble resin is a substance, selected from the group consisting of (b1) a cured polycondensation product of melamine and formaldehyde, (b2) a cured epoxide resin, (b3) a cured polycondensation product of an aromatic hydroxy compound and formaldehyde, (b4) a polycondensation product of a polyol and a polyisocyanate, (b5) a reaction product of a polyisocyanate produced by reacting a (b5, 1) polyisocyanate with water resulting in the formation of a polyurea, (b5, 2) polyisocyanate in contact with a trimerisation catalyst resulting in the formation of a polyisocyanurate, (b5, 3) polyisocyanate in contact with a carbodiimidization catalyst resulting in the formation of a polycarbodiimide, this phosphorus constituent is present in a total concentration of from about 5 to 30 wgt %, based on the total polyolefin composition to provide a polyolefin of improved thermal stability.