Process for addition of additives to polymer particles

A process for the preparation of a polymer moulding powder for rotational moulding, said process comprising:

• (i) obtaining a plurality of polyolefin polymer particles having a mean particle size of 1 to 2000 μm;
• (ii) heating a mixture of:
• A) at least one phenolic antioxidant;
• B) at least one organic phosphite or phosphonite antioxidant;
• C) at least one UV-stabiliser selected from [1,6-Hexanediamine, N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-, polymer with 2,4,6-trichloro-1,3,5-triazine, reaction products with, N-butyl-1-butanamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine] (e.g. Chimassorb 2020), [Poly((6-morpholino-s-triazine-2,4-diyl)(2,2,6,6-tetramethyl-4 piperidyl)imino)hexamethylene (2,2,6,6-tetramethyl-4-piperidyl)imino))] (e.g. Cyasorb UV 3346), [Poly((6-((1,1,3,3-tetramethylbutyl)amino)-1,3,5-triazine-2,4-diyl)(2,2,6,6-tetramethyl-4-piperidyl)imino)-1,6-hexanediyl((2,2,6,6-tetramethyl-4-piperidyl)imino))] (e.g. Chimassorb 944), Cyasorb 4042 or Cyasorb 4611;
• D) a diluent;
• and optionally
• E) a metal stearate;
• to a temperature of between 20 and 200° C.;
• (iii) depositing the mixture onto said polyolefin polymer particles;
• and optionally
• (iv) blending a metal stearate to the resulting polyolefin polymer particles if component e was not present in said mixture.