Pulverulent flame-retardant composition with low dust level, its use, and process for its preparation, and flame-retardant polymeric molding compositions

A flame retardant combination comprising, as component A, a phosphinate of the formula (I) and/or a diphosphinate of the formula (II) and/or polymers of these

• where
• R1 and R2 are identical or different and are C1-C6-alkyl, linear or branched, and/or aryl;
• R3 is C1-C10-alkylene, linear or branched, C6-C10-arylene, -alkylarylene or -arylalkylene;
• M is calcium ions, magnesium ions, aluminum ions and/or zinc ions,
• m is 2 or 3;
• n is 1 or 3;
• x is 1 or 2;
• and comprising a component B1, B2 and/or B3 wherein
• B1 is a salt of 1,3,5-triazine compound with polyphosphoric acid with a number average degree of condensation n is higher than 20 and with the melamine content amounting to more than 1.1 mole of melamine per mole of phosphorus atom, and a preferred pH of a 10% slurry of that polyphosphate salt in water being higher than or equal to 4.5, wherein the prefered 1,3,5-triazine compounds are melam, melem, melon, especially melamine, or mixtures of these compounds, and
• wherein B2 is a melamine polymetaphosphate having a sulubility of from 0.01 to 0.10 g/100 ml in water at 25° C., a pH from 2.5 to 4.5 in the form of a 10 wt. % aqueous slurry at 25° C. and a melamine content of from 1.0 to 1.1 mol per mol of phosphorus atom, wherein that component B2 is a melamine salt of a long-chain polyphosphoric acid represented by the formula (III)
• (MHPO3)n
• wherein M is melamine, represented by the formula (IV)
• C3N6H6.
• H is a hydrogen atom, P is a phosphorus atom, and the degree (n) of polymerization of said melamine salt of linear phosphoric add is an integer of at least 20, and
• wherein B3 is a composite salt of polyphosphoric acid with melamine, melam and/or melem having a solubility in water (25° C.) of 0.01 to 0.10 g/100 ml, a pH of 4.0 to 7.0 as measured using a 10% by weight aqueous slurry (25° C.), and melamine contents of 0.05 to 1.00 mol (preferably 0.05 to 0.40 mol), melam contents of 0.30 to 0.60 mol (preferably 0.30 to 0.60 mol) and melem contents of 0.05 to 0.80 mol (preferably 0.30 to 0.80 mol), respectively, per mol of phosphorus atoms.