Importance

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Abstract

Finely divided particles of II type ammonium polyphosphate (APP) which, when added to polyolefin resins, etc., afford products having a small reduction in the mechanical characteristics, a reduced particle diameter and an increased specific surface area and nevertheless, having bleed resistance and flame retardancy similar to those of conventional products, and a process for producing the particles are provided, the particles being characterized in that 80% by weight or more thereof have a particle diameter of 10 .mu.m or less and 5% aqueous solution thereof dissolved in 80.degree. C. water has 500 cps or more, and the process being a process for producing the particles by reacting ammonium phosphate with P.sub.2 O.sub.5, each in a nearly equimolar quantity, in a NH.sub.3 gas atmosphere and at an elevated temperature, comprising a first reaction step carried out in N.sub.2 gas atmosphere without feeding NH.sub.3 gas, a second reaction step of instantaneously feeding NH.sub.3 gas or a NH.sub.3 -generating substance when hot, in 3 to 90% of the stoichiometrical quantity, and a third reaction step of slowly adding NH.sub.3 gas in a quantity or more of the remainder of the stoichiometric quantity and aging therewith, to crystallize the resulting II type APP.

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