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Abstract

A two step method of preparing fire retardant thermoplastic polymer granules from fire retarding agents and thermoplastic polymers in a stationary granulating cylinder containing mixing elements mounted to a central rotating shaft which fluidizes and throws contained materials toward the center of the cylinder, forcing axial and radial flows simultaneously on the materials thereby forming granules. In the first step, a fire retarding agent is mixed with a fluid thermoplastic polymer at a temperature exceeding the solidification point of the polymer until a homogeneous mixture is formed. In the second stage, the mixture is solidified by cooling while the granulating cylinder continues to operate until the fire retardant agent is bound together in homogeneous granular form by a matrix of solid thermoplastic polymer. Suitable fire retarding agents include alumina, phosphates, borates, melamine, melamine cyanurate, metal cyanurates, and halogenated phenols. The fluid thermoplastic polymer may be a metal or aqueous dispersions. Suitable polymers include polyolefins, polyphenyls, polyamides, polyfluocarbons, polycarbonates, polyurethanes, polyesters, and polyvinylidene chloride. The method allows preparation of thermoplastic granules, suitable for melt blending with other polymers, containing as much as 90 percent fire retardant agent. The fire retardant thermoplastic concentrate granule compositions prepared by this method are new and exhibit better physical properties at high active ingredient concentrations than compositions available heretofore. These new concentrated fire retardent compositions have improved properties of melt blending with other thermoplastics to impart fire retardency thereto.

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First Claim