| 摘要 |
A polyolefin polymer powder for use in rotational molding requires the presence of stabilizers, including UV-stabilizers, to prevent degradation during processing and use. It has been found that the polymer may be stabilized by a particular blend of additives or by the addition of a masterbatch of UV-stabilizer loaded polymer particles. Also, it has been found that polymer particles made using a supported catalyst manufactured using a mechanically fluidized bed, a product particularly suitable for rotomolding may be produced. Thus, the invention provides a process for the preparation of a polymer molding powder comprising (i) impregnating a mechanically fluidized porous particulate support material with a catalyst and polymerizing a monomer or monomer mixture in the presence of the catalyst-impregnated support material to give olefin polymer particles; and then either (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-stabilizer; 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 particle if component E was not present in said mixture; or (iia) obtaining a second polymer; (iiia) intimately mixing said second polymer with a UV-stabilizer to produce a plurality of UV-stabilizer loaded polymer particles, e.g. by admixing stabilizer and particles of said second polymer followed by melting and grinding the resultant admixture; (iva) admixing polymer particles obtained in step (i) with UV-stabilizer-loaded polymer particles obtained in step (iiia).
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